What sensor will stop a car from starting?

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

An engine stall condition can be caused by many different systems or components.

Photo License: CC0 Public Domain

What Is Wrong With My Car?

When your car engine starts but stops afterwards, whether immediately or after a few minutes, there could be one or more specific systems or components behind the failure. For example:

• the ignition or injection system;
• a low idle speed in need of adjustment;
• a maladjusted carburetor;
• vacuum leaks;
• one or more bad sensors.

To make matters worse, stalling may happen under one or more operating conditions. For example, the engine may:

• stall as soon as it starts,
• stall during idle,
• stall when warm, or
• stall intermittently under any condition.

The conditions associated with your stalling problem will give you clues as to what systems or components are causing your problem.

So the best way to start your diagnostic is to identify, when possible, the conditions under which the stalling occurs, and focus your attention on those systems or components associated with the failure under that particular condition.

How to Investigate and Diagnose Your Problem

The following sections discuss different operating conditions associated with stalling, and which systems and components are most likely to cause stalling under those conditions. The last section focuses on what to do when stalling happens intermittently and seemingly randomly.

So, start by checking those components or systems in the section that best describes your particular engine problem, and then, if necessary, move on to systems or components described in other sections, especially if you suspect these systems need maintenance or have given you problems in the past. This approach will make it easier for you to diagnose the problem much faster and will work in most cases.

Check for Codes

Also, be sure to check the computer system for any diagnostic trouble codes (DTCs) that might be stored in memory, whether the "check engine" light has come on or not. One or more sensors may have triggered a pending code. If you don't have a scanner tool, you may be able to take your vehicle to a local auto parts store to get the codes retrieved, or the store may lend you the scanner. Better yet, buy a relatively inexpensive but quality automotive scanner from your local auto parts store or online.

Tip: The Anti-Theft System

If you've seen the anti-theft light blinking recently, make sure the anti-theft system is working properly. The system itself can be the source of the problem. Sometimes you need to reset the system (make the system go through a re-learning procedure) to get the engine working right again. If necessary, consult your vehicle repair manual.

Index

1. If Your Engine Stops Immediately After It Starts

2. If the Engine Stalls at Idle

3. If the Engine Stalls at Idle Unless You Press the Accelerator

4. If the Engine Starts When Cold but Stops When Warm

5. If the Engine Stalls Intermittently

Check the fuel filter.

Photo courtesy of Diego Torres Silvestre on Flickr

1. If Your Engine Stops Immediately After it Starts

Your engine may stop as soon as you let the key return from the Start to the Run position. Most of the time, this condition points to a badly clogged fuel filter or an ignition switch in need of adjustment or with worn/burned contacts.

A quick test to see if you have a problem with the fuel system is by using carburetor cleaner or starting fluid:

1. Carefully disconnect the air cleaner outlet tube from the throttle body.
2. Ask an assistant to start the engine.
3. As soon as the engine catches and the ignition key returns to the Run position, spray some carburetor cleaner into the throttle body.
4. If the engine idles momentarily with the carburetor cleaner, there may be a problem with fuel delivery.

The problem can be with the fuel filter, fuel pump, ballast resistor, or fuel pressure regulator.

Start with the fuel filter. When was the last time you replaced the filter? Check the fuel filter service interval in your car owner's manual or repair manual. If the fuel system uses an in-line filter:

• Remove the filter.
• Blow through the filter in the direction of fuel flow.
• If air goes through with difficulty, or not at all, there's your problem

When necessary, use a fuel pressure gauge to check system pressure. Follow the instructions in your vehicle repair manual. If you don't have the manual, you can buy an inexpensive, aftermarket copy at your local auto parts store or online.

Other components that can cause you trouble are:

• fuel pump
• fuel injectors
• engine coolant temperature (ECT) sensor (see the next section)
• fuel pressure regulator
• crankshaft position (CKP) sensor

Usually, a bad CKP will trigger the check engine light (CEL). So scan the computer for DTCs if you haven't done so yet.

To do a quick check for potential CKP problems:

• While, cranking the engine, pay attention to the tachometer on your dashboard.
• If the RPMs remain at zero, this may point to a problem with the CKP sensor.

Check your vehicle repair manual to help you test the crankshaft sensor, if necessary. Even if the sensor itself is good, there could be an electrical open or short in the circuit.

Check the ignition switch:

If you seem to be getting good fuel supply, and the previous tests didn't yield any clues, try checking the ignition switch. Ignition switch contacts wear out over time.

Sometimes, you can detect problems with the contacts by holding the key forward in the Start position when cranking the engine. The engine may catch in the Start position, but as soon as you let the key return to the Run position, the engine dies.

1. First gain access to the ignition switch. Consult your vehicle repair manual.
2. Make sure the switch is properly connected to the electrical connector.
3. Squeeze the switch and electrical connector together with your hand as you try to start the engine.
4. If the engine starts and remains idling while holding the switch and connector together, you need to properly connect the switch.

Even if this quick test doesn't yield results, you will still want to troubleshoot the ignition switch. Your vehicle repair manual may help you here.

Check for throttle body and throttle plate buildup:

Also, check your throttle body and throttle plate for coking. Carbon buildup will prevent proper operation of the throttle valve. If the valve doesn't have free movement, it can cause a rough idle and stalling with light buildup. Coking usually causes the engine to die immediately after the engine starts.

You can use carburetor cleaner to remove carbon buildup from the throttle bore and valve, if necessary.

Verify that the ignition system has a good, strong spark.

Photo license: CC0 Creative Commons

2. If the Engine Stalls at Idle

Various components and maintenance issues may cause an engine to stall when idling. The source of the problem may differ with the type of engine model or configuration.

Ignition System Problems

The system may have a weak spark or the spark may fail to reach the spark plugs.

• Start by checking the service schedule for the spark plugs and spark plug wires.
• Remove and check one spark plug at a time.
• Check the electrodes' gap using a wire gauge and compare to specs in your vehicle repair manual.
• A plug that burns the air-fuel mixture correctly has a brown to grayish-tan color. Other colors may indicate problems with the fuel, ignition or even mechanical problems.
• A wet plug may indicate too much fuel reaching the cylinder, or a mechanical problem that is leaking oil into the combustion chamber like worn-out rings, cylinders or valve stem seals.
• Then, check the spark plug wires and ignition coils with the help of your vehicle repair manual.
• If your engine uses a distributor, check the cap as well for cracks, carbon traces, and oil contamination.

Bad canister vent valve:The evaporative emissions (EVAP) control system routes fuel vapors into a canister and then to the intake manifold where they are burned along with the air fuel mixture. But a system failure, especially a failure of the canister vent valve, can cause the engine to stall at idle or during acceleration. Consult your vehicle repair manual for valve testing procedures in your particular vehicle model.

Other system components to check, depending on your particular model:

• purge solenoid or valve
• canister
• relief valve
• hoses

Checking the PCV Valve:The positive crankcase ventilation (PCV) system purges blowby gases from the engine. Most PCV systems make use of a small valve to route blowby gases back into the intake manifold to be re-burned. Over time, the valve may get stuck open, causing too much air to flow into the intake manifold during idle or acceleration, which can cause the engine to stall.You can easily remove the valve and check it by shaking the valve. If the valve doesn't rattle, probably the valve is stuck. But this common test doesn't work for all models. Consult your vehicle repair manual, if necessary.

A Bad Throttle Position Sensor (TPS)

The TPS monitors the angle opening of the throttle valve and sends this information to the electronic control module (car computer). The computer uses this information, along with signals from other sensors, to adjust air-fuel ratio, ignition timing and other outputs. Most TPS units use a variable resistor with several contact points that can wear out and fail after miles of service. When the contacts open, it may cause the computer to lean the mixture too much and stall the engine. A bad TP sensor usually triggers a diagnostic trouble code (DTC). So you can retrieve the code from the computer using a scanner tool.

Whether or not you find a trouble code for the TPS, it's a good idea to test the sensor using a digital multimeter:

1. Unplug the sensor electrical connector.
2. With the engine off, measure resistance across the sensor terminals with the throttle in closed position, at half throttle, and at full throttle.
3. Compare your resistance measurements to the specifications listed in your vehicle repair manual.

One or more bad fuel-injection components may cause the egnine to stall.

Photo courtesy of Vegavairbob on Wikimedia

Checking the IAC (for Engines With Multiport Injection Systems, Most Modern Engines):In most cases, the problem here is associated with the idle air control (IAC) valve.

The IAC valve is controlled by the computer and allows air to bypass the throttle valve under idle or cold temperature conditions to prevent a rough idle or keep the engine from stalling. You can test the IAC valve using a digital multimeter:

1. First, unplug the IAC electrical connector.
2. Turn the ignition key to the On (run) position but don't start the engine.
3. Set your voltmeter to 20 Volts range (or above 15 Volts) on the DC (direct current) scale.
4. Connect your black meter lead to ground (engine metal surface or battery negative post, for example) and with the red meter lead probe the terminals on the harness side.
5. You should get around 10 to 12 volts, approximately, from one of the terminals. This is the incoming signal from the engine control module (car computer). If not, there are problems in that side of the circuit.

Now measure the condition of the valve by measuring resistance across the IAC connector terminals.

1. Set your voltmeter to ohms for this measurement.
2. You should get anywhere from 6 to 13 ohms of resistance.

To check for a possible internal short:

1. Check for resistance from each IAC connector terminal and the IAC valve body with your voltmeter.
2. You should get around 10,000 ohms of resistance.

Checking the internal physical condition of the IAC valve:A blocked IAC may cause the engine to die as soon as it starts if the valve sticks close. IAC valves may fill with carbon deposits overtime, preventing the pintle from moving, or blocking valve passages.

On most vehicle models, the IAC valve is readily accessible and can be removed easily by unscrewing a couple of mounting bolts.

1. First, turn the ignition key off and remove the key.
2. Unplug the IAC valve electrical connector.
3. Unscrew the valve mounting bolts and remove the valve from the vehicle.
4. Check the valve's pintle and housing for carbon buildup. If necessary, clean the valve with carburetor cleaner and a soft rag to remove deposits.
5. Also, check the valve O-ring. It should be soft and in good condition. Otherwise, replace it.

Consult your vehicle repair manual for the recommended testing procedures for your particular vehicle model, if necessary.

Your particular fuel injection system may have other necessary adjustments. For example, you may need to adjust

• the idle speed
• the throttle cable
• the throttle plate stop
• the idle air-fuel mixture

Consult your vehicle repair manual, if necessary.

Troubleshooting the ECT (Engine Coolant Temperature) Sensor

The ECT measures engine operating temperature and sends this information as electrical data to the computer. The car computer uses this information, and information from other sensors, to adjust ignition timing for better engine efficiency.Thus, a bad ECT sensor can have a direct impact on engine performance. If the sensor causes a lean air-fuel mixture the engine may idle rough or stall.Most ECT sensors use a thermistor to vary the voltage signal sent to the computer according to engine coolant temperature. The higher the coolant temperature, the lower the sensor resistance and higher the signal voltage.

To test the ECT sensor:

1. Locate the sensor. It's usually close to the thermostat housing.
2. With the engine turned off and cool, unplug the ECT sensor electrical connector.
3. Set your digital multimeter (DMM) to the ohms scale and measure resistance across the sensor terminal. Make a note of the resistance value.
4. Plug in the sensor electrical connector and start the engine. Let the engine idle for about 15 or 20 minutes so that it reaches operating temperature.
5. Shut off the engine.
6. Unplug the ECT electrical connector and measure resistance across the sensor terminals as you did in step 3.
7. This time, sensor resistance should be considerably lower. For example, depending on your particular sensor configuration and engine model, the sensor may have 40K ohms when the engine is cold but 2K ohms when hot.
8. Compare your results to the specifications listed in your vehicle repair manual.

A failing ECT sensor can trigger the check engine light. If your sensor checks Okay during your tests, but the computer says there's a problem with it, check the sensors circuit between the ECT and the computer for bad connections or damaged wire.

Also, check that the computer is sending the correct reference voltage to the sensor.

• Unplug the ECT sensor electrical connector.
• Turn the ignition key to the On position, but don't start the engine.
• Measure the voltage at the harness connector (the one leading to the computer) with your voltmeter.
• Usually, you should read about 5 volts at the connector. If not, there's a problem in the circuit.

Checking for a Stuck EGR ValveThe exhaust gas recirculation (EGR) systems reintroduces exhaust gases into the combustion chambers to reduce engine temperature and poisonous emissions.It is common for the EGR valve passages to get blocked from carbon buildup. Carbon deposits may prevent the valve from closing, causing the engine to stall at idle. Also, an EGR valve may leak through the base, causing the engine to stall at idle, at deceleration, or during a quick stop.

If you've never checked under the valve, or it's been a few years since you last checked, it might be a good idea to take a look now. But make sure to have on hand a gasket replacement. You may need to install a new one. If you can't find one for your particular vehicle model, you still can buy gasket paper at your local auto parts store and make the gasket yourself.

• Most EGR valves are accessible and not difficult to remove. Check the EGR valve configuration for your particular model, though, to make sure you have all the tools necessary for the job. Usually, all you need is a couple of wrenches, a ratchet, the appropriate socket sizes and, sometimes, a pipe wrench to disconnect the valve from the exhaust pipe. Consult your vehicle repair manual, if necessary.
• Remove carbon deposits from under the valve and intake ports using carburetor cleaner. Make sure not to allow carburetor cleaner to reach the valve diaphragm or any electrical circuits, depending on your particular model, or you may ruin the valve.
• Reinstall the valve using a new gasket, if necessary.

Checking the EGR Valve:Depending on your particular EGR valve configuration, you probably can stick your finger through the underside of the valve and try to move the internal diaphragm. If the diaphragm doesn't move, it may be stuck.

Here are a couple of alternative methods to check for diaphragm movement:

• Operate the accelerator linkage with your hand to increase engine speed. You may be able to see the diaphragm moving using a mirror placed under the EGR valve. If you can see the diaphragm with the mirror, but you can't see it moving as you operate the accelerator linkage, the diaphragm might be stuck.
• You can also use a hand-held vacuum pump. You can do this test with the engine off and using a mirror to watch diaphragm movement. Disconnect the vacuum hose form the valve and connect the vacuum pump instead. Apply about 15 in-Hg of vacuum to the EGR valve while watching for diaphragm movement with the mirror. If the diaphragm doesn't move, it might be stuck.

Another cause for the valve diaphragm to fail is wear or damage that causes it to leak exhaust gases. A quick way to test for a leaking diaphragm is using carburetor cleaner.

• Block the wheels using wooden blocks.
• Set your transmission to Park (automatic) or Neutral (standard).
• Start the engine and pop the hood open.
• Spray a quick burst of carburetor cleaner under the valve, towards the diaphragm.
• If the engine RPMs increase when you spray, the diaphragm is leaking and you need to replace the valve.

Bad Catalytic Converter

A bad catalytic converter can also cause you problems at idle. Depending on the particular problem, it may show other symptoms as well:

• a smell of rotten eggs
• rattling sounds
• poor engine power

One of the most common problems with a catalytic converter is a plugged unit. The internal substrate becomes partially restricted or disintegrates.Usually, problems with the catalytic converter trigger the check engine light (CEL). The computer may store a P0420 through P0423 code. If you find a catalytic-converter-related code, do troubleshoot the catalytic converter before replacing it, to confirm that the cat is in fact bad. Catalytic converters are expensive and you need to make sure that some other components is not involved in the problem. If necessary, consult your vehicle repair manual.

Checking the IAC on Vehicle Models With Throttle Body Injection (TBI) Systems:

Many vehicles equipped with TBI systems also have an IAC valve controlled by the computer.

• You can use the test described in the previous section, if your vehicle has an IAC valve.
• Besides, some of these systems may have an idle speed adjustment (consult your repair manual),

Usually, you can adjust idle speed by hooking up a tachometer (some digital multimeters have this feature) to the engine. Then, you can turn the idle speed screw on the throttle body or carburetor until the RPMs are set according to specifications.

Carburetor worn out components can cause the engine to die.

Photo courtesy of Uberprutser on Wikimedia

Diagnostics on Vehicles With a Carburetor

A stalling issue usually points to a maladjusted idle mixture screw. To reset the screw:

1. Locate the idle mixture screw.
2. With the engine off, bottom the screw.
3. Back out the screw 2 1/2 turns.
4. Start and idle the engine.
5. Make the final adjustments until you get a smooth idle.

On some carburetor models, you may also need to adjust curb idle speed. Consult your repair manual.

On carburetors in need of maintenance or worn parts, there can be several components that need attention. For example, you may need to check:

• throttle dashpot adjustment
• bowl fuel level
• idle system for clogging
• carburetor flooding
• vacuum leak
• float needle valve operation
• restriction in the air cleaner

Consult your vehicle repair manual.

Sometimes, using the accelerator pedal can keep your engine from stalling.

Photo courtesy of ScrewsHirsch on Wikipedia

3. If the Engine Stalls at Idle Unless You Press the Accelerator

This may indicate problems with the fuel system. The following video shows an engine with this problem.

If your engine has a throttle body injection (TBI) system:

1. Pop the hood open and remove the air cleaner assembly so that you have access to the throttle body.
2. Turn the ignition key to the On position but don't start the engine.
3. Take a look at the injector(s) on top of the throttle body.
4. If the injector(s) is leaking fuel, then you need to replace it. The injector may have a worn or inoperative return spring or valve; or dirt may have the valve stuck in the open position.

Also, check fuel system pressure using a fuel pressure gauge. Consult your vehicle repair manual.

If your engine has multiport fuel injection system:

Checking fuel injectors for leakage on this type of system can be tricky, depending on your particular vehicle and engine model. Consult your vehicle repair manual about detaching the fuel injectors from their ports for inspection, if necessary.Another potential problem could be the fuel pressure regulator.

1. Locate the pressure regulator on the fuel rail.
2. Detach the vacuum hose from the pressure regulator
3. Closely inspect the regulator port and inside the vacuum hose for signs of fuel
4. If you notice gasoline in either component, replace the fuel pressure regulator.

Fuel delivery system leaking:

Although rare, the cause of a stall may come from a leak in the fuel delivery system, specially the fuel pump. The engine may receive fuel but not enough to keep the engine running.

The leak may be located in the fuel pump assembly, or along the way up to the fuel rail.

Check for strong fuel odors or wet spots around the fuel rail, fuel hoses and tubing, around connectors. Also, you may need to check the fuel pump assembly.

See your repair manual for more fuel system tests, if necessary.

A bad electrical circuit in a coil or ignitino moduel may cause the engine to stall when warm.

Photo courtesy of Cschirp on Wikimedia

4. If the Engine Starts but Stops When Warm

An engine can also stall when reaching operating temperature or a few minutes after a cold start.

Sometimes, this can be a sign of problems with an:

• ignition coil
• ignition module (depending on your vehicle model)
• fuel pump
• crankshaft position (CKP) sensor
• camshaft position (CMP) sensor

It usually happens when an electrical "open" exists in the internal circuit of one of these components. After a few minutes of operation, heat may cause a coil or wire to expand and loose electrical contact. You may not be able to start the engine again until the heat in the troubled component has dissipated. Later, when heat causes the open to manifest itself again, the engine may stall again.Trying to find the faulty component can be hard. But here are a few simple procedures to get you going.

When the engine dies, check to see if you have spark:

1. Disconnect one of the spark plug wires from its spark plug.
2. Place the tip of the wire about 2 inches away from the engine surface or a metal bracket using a pair of insulated pliers.
3. Have an assistant crank the engine and see if there's spark.
4. You should see a strong, blue spark between the tip of the wire and ground.
5. If there's no spark or you need to have the wire about 1/4 inch close to ground for a spark, probably the fault is with the ignition module, ignition coil, CKP or CMP.

When there's spark, check for the presence of fuel:

1. If you have a fuel pressure gauge or can borrow one from your local auto parts store, connect the gauge and idle the engine.
2. Monitor the gauge and see if the fuel system looses pressure when it stalls. If it does, you may have problems with the fuel pump or a system component.

You can also check for weak fuel pressure using this simple method:

1. When the engine stalls, remove the air cleaner assembly and spray some carburetor cleaner or starting fluid at the throttle and try to start the engine or have an assistant crank the engine while you spray a burst of carburetor cleaner into the throttle body.
2. If the engine catches or starts for one or two seconds when you spray the fluid, then you may have a problem with the fuel pump or another system component.

Check the fuel system with the help of your vehicle repair manual.

A bad circuit in a CMP can prevent the engine from idling.

Photo courtesy of Teresa Trimm on Flickr

5. If the Engine Stalls Intermittently

If your engine stalls intermittently, under a variety of conditions, suspect these components:

A Bad Camshaft Position Sensor

A bad camshaft position (CMP) sensor can produce different types of symptoms and cause the engine to stall immediately after starting or intermittently.

A bad camshaft sensor is likely to trigger the check engine light (CEL). Even if you don't see the CEL illuminate, scan the computer memory for diagnostic trouble codes (DTCs). Common bad camshaft DTCs range from P0340 to P0344.Consult your vehicle repair manual to locate and test the camshaft sensor, if necessary.

Misfires

Engine misfires are another cause for an engine to stall. Misfires make popping sounds and can cause engine to jerk or vibrate. Other symptoms include:

• increased emissions
• increased fuel consumption
• difficulty starting
• stalling

If you've noticed engine misfires, this might be the cause for the engine to stall. Check this other article to help you diagnose the source of the misfire.

Clogged air filter

You can remove the air filter and check it. Air filters trap dirt and dust from the stream of air flowing into the intake manifold. To check the filter:

1. Remove it from its housing.
2. Place the filter against the sun or a good source of light.
3. If the light can barely get through the filter element, or not at all, the filter is clogged and preventing proper air flow into the engine, causing it to stall.

Vacuum LeaksAn engine stalling issue can also come from a vacuum leak problem.A vacuum leak can upset sensors or actuators that depend on vacuum for operation: for example, the manifold absolute pressure (MAP) sensor, exhaust gas recirculation (EGR) valve or mass air flow (MAF) sensor. The leak can happen because of loose or damaged hoses or gaskets.Testing one of these sensors requires checking the vacuum hose, electrical connection and wires, and testing the sensor itself. Consult your vehicle repair manual. On a MAF sensor, check for a dirty sensing element. You can clean the sensing element using MAF sensor cleaner or electrical contact cleaner. Follow the product instructions when using this type of cleaner.Vacuum leaks usually make a hissing sound but you may need a mechanics stethoscope or a length of hose to listen and locate potential vacuum leaks.

• Check that all vacuum hoses are properly connected.
• Check the condition of each hose.
• Use the stethoscope or length of hose to listen for leaks along the vacuum hose and connections.
• Trace each hose with your hand to feel for potential damage: soften, harden or irregular spots.
• Check for vacuum leaks around the intake manifold gasket and throttle body as well.

It's Worth Trying to Diagnose An Engine That Shuts Off

If your engine starts but won't stay running, you want to make an accurate diagnosis as soon as possible. Making a diagnosis can be hard, especially when you don't have much experience in car repair and the source of the problem can be in one of several systems. Use the strategies outlined in this guide. They'll help you repair your car faster by having you concentrate on those systems more likely to give you trouble.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

Question: Where is the problem when, after driving, I stop and it doesn't start until I give some time. How would you diagnose my car's problem if my car will start again after some time?

Answer: If the engine cranks but won't start, check for spark and fuel pressure. If it doesn't crank at all, check the battery condition.

Check for DTCs codes, even if you haven't seen the check engine light come on. There might be a pending code. Usually, when the engine warms up and then stops, it is an indication of a problem with an ignition coil, ignition module or even the fuel pump. Allowing time to cool, the component will function again. Try some of the tests described in section IV of the post.

Question: What does it mean when the car gets started when it is cold but not when it is hot?

Answer: Check the connections, wires and cables in the staring circuit. They should be clean and tight.

Question: My car won’t turn over. I used starting fluid and it started up, then immediately cut off. What can be the reason for that?

Answer: If the engine doesn't turn over, there could be something wrong with the starter motor or the engine is seized. But, if the engine fires up with starting fluid, then check for fuel pressure. Probably not enough fuel is getting to the cylinders.

Question: My car runs fine for a few minutes, then starts sputtering and loses a lot of horsepower. It doesn’t stall but the engine sounds rough like an old 80s car. A night of rest lets the car become drivable again for a few minutes but then the issues show up again. I’ve changed the spark plugs, plug wires, distributor cap and rotor, air filter, cleaned the maf sensor and changed the throttle position sensor. What else could be the problem?

Answer: The problem seems to be temperature related. This usually happens with a faulty ignition coil, ignition module or fuel pump motor's coil. The coil device or temperature sensitive electronics will begin to fail from an electrical open. Have the ignition coil, ignition module and/or fuel pump checked.

Question: Why does my car start and idle for 3-5 minutes before dying? The spark plugs and fuel filter were replaced. The carburetor was taken off, checked and cleaned. The distributor was taken off and cleaned as well. It still does not want to idle entirely after starting, so it cannot drive at all. Please help as the mechanic can't seem to figure out whats wrong with my car.

Answer: There could be several causes for this, so try the following:

Have the ignition system checked to make sure it has a good spark.

Check the fuel system- fuel pressure

Check the canister vent valve, PCV valve, TPS sensor, and IAC valve.

Question: May car engine stalls while idle unless you press the accelerator. This indicates problems with the fuel system. How do you fix the fuel system?

Answer: If you know the problem is in the fuel system, first make sure you have replaced the fuel filter. Then start by testing for fuel pressure at idle. This other post can help:

//axleaddict.com/auto-repair/How-to-Test-a-F...

This could lead to a bad pressure regulator or fuel pump or bad injector(s).

Question: My VW T4 runs completely fine, but when it’s been in hot weather, or indeed damp weather, it starts and instantly dies. This is intermittent. Sometimes after it dies, if you try again it can start straight away, or you can be waiting for half an hour before you can start it. Once started it runs fine. Do you have any ideas?

Answer: Usually, when a car struggles to run in damp weather, the problem is with the ignition system. A coil or cable in the system is probably leaking the spark to ground.

Question: My car was diagnosed as having a bad fuel pump. After a new fuel pump was put in, it got four miles down the road, idled out, and died again. The car will not crank until about 15 minutes after it happens. What do you think could be the cause of this problem?

Answer: If you mean the engine will not turn over, the problem seems to be in the starting system circuit. This other post may help:

//axleaddict.com/auto-repair/bad_starter_sym...

If the engine cranks but won't start after the car has been driven about four miles (engine turns over but won't start), then possibly the ignition coil or ignition module is bad. In this case, the coil reaches operating temperature, coil breaks open and the car stops. Once the coil cools, the broken wire makes contact and you are able to start the engine, and the cycle repeats.

This other post may help you test the ignition coil:

//axleaddict.com/auto-repair/How-to-Test-an-...

If your car has a coil on plug configuration, check the repair manual for your particular model to test the coils. You can also check for spark right after the engine refuses to start. If there's no spark, you know the problem is in the ignition system (or crankshaft-camshaft position sensor) and you are on the right track.

Question: My truck starts and within 6 seconds it dies. I cannot provide more gas to keep it running. If I unplug the Air Flow sensor it will start and idle but again if I give it gas it dies. I also started with changing out the fuel filter. No difference. Any thoughts?

Answer: If you are able to start the engine right after it stalls with the MAF sensor disconnected, probably this sensor is dirty or faulty or another sensor is not sending the correct signal the computer expects, probably the throttle position sensor. Download trouble codes even if you don't see the check engine light on. There could be a pending code that can help you.

Question: I have a 2013 Chevy Sonic. For the last 5 months, my car has stalled during driving and when in idle or when I stop at red light and stop signs. Also, it fails to turn over after putting gas. It will turn over fine, but it won't stay on. I've had my fuel injector cleaned and inspected. I've had my O2 sensor replaced as well. Do you have any ideas what this could be?

Answer: You may be dealing with a vacuum leak or a faulty sensor like a MAP or MAF sensor. You may also have a problem in the fuel system or with the fuel pump. Have the pump checked before replacing it.

Question: What can make a car just switch off and the battery light to go on in the instrument panel? I have tested the battery and it is good.

Answer: The most common reason for this is a bad alternator. Have the charging system tested.

Question: What would be the problem if the engine dies at intersections when reverting to first gear? I replaced the carburetor.

Answer: The carburetor may need an idle adjustment. Check the manual, if it came with it. Or look for it online.

Question: I have a 1993 Caprice Classic. And about 4 months ago, I mistakenly put the wrong grade of gas in. Since then, I've had issues as far as when upon starting it idles very low and then too high until it does normally after about 30 or so seconds. Once I drive it, I can go so far, and once I come to a light or stop sign it eventually cuts off but starts back up immediately. I've heard that it could be a number of things including bad fuel injectors. What's your expert opinion on this?

Answer: It seems like an electrical problem. Try downloading trouble codes, even if the engine light doesn't come on. There could be a problem with a sensor.

Question: Why does my car only start in the morning?

Answer: Check for any DTCs in the computer memory first. You may need to take a look at fuel pressure or ignition spark after the car has warmed up. Maybe there's a problem with the fuel pump or an ignition coil.

Question: Two days ago my truck shut off immediately after starting it up. The truck will accelerate by itself then shut off. It fails to restart after a few tries then it will start and run. Two months ago, it shut off while driving, so I replaced the battery and alternator and no problems for two months. What could cause my truck to shut off after starting up?

Answer: It seems like a faulty sensor. Intermittent faults can be hard to diagnose, though. But you may want to check the battery cables, engine grounds, ignition switch connector, and wiring, and faulty wiring in a critical sensor the computer relies on to operate the fuel injectors, crankshaft, throttle position sensor or camshaft sensor, for example. If the engine shuts off as if turning the ignition switch off, most likely the problem is in a circuit. A voltage drop test might help:

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Question: 90 Chevy. I replaced the fuel pump, fuel filter, fuel pump relay and throttle control position sensor. Truck dies at random. If watching the throttle body when running, fuel just stops. I cycle the key and it works again. If I don't cycle the key, no fuel comes out. Any ideas?

Answer: If the engine dies as if turning off the ignition key, most likely the problem is a loose wire or bad connection either on the fuel pump circuit or throttle position sensor circuit. Double-check those circuits, including wiring harness and connectors. Cycling the key may point to corroded or loose wire(s) that have too much resistance and are getting hot. Visually check for corrosion and tug at the wires on the connectors to make sure they are not loose or dirty.

Question: My engine starts, then after a few seconds engine is off by itself. And then the dashboard displays an auto protection alarm. What could be the cause of this remark?

Answer: The message comes from the car's computer. It's trying to protect the engine because of a serious fault it has detected. Download the trouble codes from the computer memory. They should give you an indication of the problem.

Question: I have a 2005 Park Avenue that keeps stalling randomly. At first, it would only stall while warming up but ran fine after it was restarted. Now, it starts and will stall while driving. Sometimes I can drive across town before it stalls, and sometimes I can only make it a few blocks. After it stalls, I have to wait about an hour before I can keep it running. Should I start with the crank position sensor?

Answer: Check your camshaft position sensor. There are other items you need to check as well like misfires, vacuum leaks, and a blocked air filter.

This other post on vacuum leaks diagnosis may help.

//axleaddict.com/auto-repair/How-to-Find-and...

Make sure to scan your computer memory for trouble codes, even if the check engine light is not on. There could be pending codes that may guide you here.

If the engine stalls after it reaches operating temperature (about 15 to 20 minutes), there could be a problem with the fuel pump or an ignition module.

Question: I had the fuel injectors cleaned, fuel pump checked, relay checked, new MAF sensor, new Crank and camshaft sensors, new ignition switch, and cleaned the throttle body with a carb cleaner. The alternator is good. New starter. It hard starts with starter fluid; I pushed the gas pedal a good 10 times with zero reaction from the rpms. Then the car died seconds later. I cannot figure it out. What could it be?

Answer: It seems like a bad sensor. Try downloading trouble codes and see if you get a pending code, even if the check engine light is not on. There could be a problem with the throttle position sensor (TPS). If the computer doesn't get a signal from this sensor, it may not fire up the engine.

Question: With the car on jacks on an incline, the engine was running fine. I tried to drive it to a shop the next day. It started fine, but within a minute it just shut off. No warning or sputter, just dead. I pushed it back to the inclined driveway and then it started fine. Could it be that what little oil was there pooled up towards the back of the engine and wasn't getting to the pump?

Answer: Some models will shut off the engine if there's not enough oil pressure. This is a safety measure to prevent severe engine damage. If there's not enough oil, add some and try again. If you think there's a problem with oil pressure, this other post may help:

//axleaddict.com/auto-repair/What-Causes-Low...

Question: Why does my engine crank but won't stay running?

Answer: There could be a fault in the injection or ignition system, a vacuum leak or some other fault. Check for trouble codes, even if you don't see the check engine light on. A sensor might be faulty as well.

Question: My engine is a Toyota 5A FE and has no problem starting at home (outdoor Street parking) even on a very cold morning. However, it cranks and instantly stalls when I try to start it at work and only when I'm at work (Covered Parking). Any reason why that might be?

Answer: It's possible the EGR or PCV valve is sticking open.

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//axleaddict.com/auto-repair/How-to-do-a-PCV...

Download trouble codes, even if you don't see the check engine light on. There could be a problem with a sensor as well. Hope this helps.

Question: I have a 2012 Ford Focus. After getting gas and about 10 miles (16.09 km) down the road, the car started to lose power and then stalled. Got it started, drove a little and it did the same thing. Finally, I made it home. It stalled again and now won’t start at all. I never had a problem until I put gas in it. My Ford mechanic said I need a new computer system. Could my Ford Focus' loss of power be something other than the computer system?

Answer: First, make sure you got fuel pressure (bad fuel pump or fuel pressure regulator, clogged fuel filter). Download trouble codes, even if the engine light is not on. There could be a pending code on the computer's memory. A bad sensor can prevent the engine from starting, like a faulty crankshaft, camshaft or throttle position sensor.

Question: When I stop the car and then come back to it after only a brief period of time, it will only stay on if I recall the engine. But once I can get it going for a little bit, it stays on and runs great and idles better than it has in years, but no one touched anything on the engine. Is it the fuel delivery or something more sinister?

Answer: Doesn't seem like a fuel system issue. Probably an issue with the idle air control (valve or solenoid) or a sensor, possibly the throttle position sensor, that is not sending the correct signal to the computer. Try downloading trouble codes, even if the check engine is not on. There could be a pending code. You may also be dealing with a bad wire or connector.

Question: When, after driving, I stop, it doesn't start and the engine light comes on until I give some time. How would you diagnose my car's problem if my car will start again after some time?

Answer: Start by downloading trouble codes. If the check engine light is coming on, there could be a faulty sensor triggering the light. Make sure to test the system or sensor indicated by the code before replacing any components. Hope this helps.

Question: My gear shift lights are not indicating on the gear after changing the gearbox and mechatronics. And we are failing to start the car Golf 5 1.9 TDI. What could be the problem?

Answer: If the engine is not cranking, there could be a problem in the starting circuit, perhaps at the ignition switch. That could also explain why you are not getting the indicator lights. This other post may help:

//axleaddict.com/auto-repair/How-to-Use-Volt...

it'll be a good idea to have the diagram for your particular model. If you don't have the repair manual, you can get one at your local auto parts store or online.

Question: Would a speed sensor cause stalling?

Answer: Usually, you'll notice issues with the transmission, brakes, speedometer, and check engine light. Try downloading trouble codes from the computer, even if you don't see the check engine light on. If there are no codes, this other post may help:

//axleaddict.com/auto-repair/No-Trouble-Code...

Question: Hyundai ix35 2013 auto. The car starts and dies. I took out one of the airflow sensors and started the car. It remains on but as soon as I put the sensor back, the car dies. Please advise?

Answer: Most likely the air flow sensor is faulty. Try testing the sensor and, if necessary, the circuit, to make sure it's bad. This other post may help:

//axleaddict.com/auto-repair/How-to-Test-a-M...

Question: My BMW 1 series cuts off while driving, the engine will start and cut off after few minutes, what could be the problem?

Answer: This other post may help:

//axleaddict.com/auto-repair/Car-Dies-While-...

Question: My car starts and the check engine light disappears. As the engine temperature rises, the check engine light appears and my car dies. What’s the answer?

Answer: Check the computer for trouble codes. If a sensor is faulty, most likely it's triggered a code. With temperature-related issues, an ignition coil, fuel pump motor or sensors like camshaft and crankshaft are common.

Question: When I try to start my Mazda, it takes several times of it trying to turn over then it starts. But sometimes it shakes and makes loud noises and cuts off unless you press the gas a little bit. Then it's good. The fuel pressure was checked and it is good. Why would my Mazda have trouble starting?

Answer: Seems like there is a problem with a sensor or the starting circuit. Try downloading any possible trouble codes, even if the check engine light is not on. This other post may help as well:

//axleaddict.com/auto-repair/How-to-Use-Volt...

Question: My car does not stay running until it comes up to operating temperature, what could be the problem?

Answer: There could be a problem with the MAF sensor not sending the correct signal to the computer.

//axleaddict.com/auto-repair/How-to-Test-a-M...

Usually, cleaning the sensor element solves the problem, using a MAF sensor cleaner. Other times the sensor itself has failed and needs replacement.

Other sources of trouble are the throttle position sensor,

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bad fuel pressure

//axleaddict.com/auto-repair/How-to-Test-a-F...

engine coolant temperature sensor

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stuck open thermostat

//axleaddict.com/auto-repair/car-thermostat-...

Question: My engine starts and runs at high idle, BUT will not idle once warmed up. The only way I can keep it running is to up the rpm to around 1200 or more. I have checked plugs, wires, vacuum lines, replaced coil. I removed the gas line from carburetor and I can fill a bottle slowly as I turn the engine over - mechanical pump. Should I replace the carburetor? It is a 4 barrel Rochester Quadrajet.

Answer: If the engine starts at high idle and then dies while it gets warmed, it's possible there is a vacuum leak. If you notice a drop in RPM before it dies, the choke may need adjustment (too tight), the carburetor may be flooding, or the float level is very high.

Question: Why does my car shut off when I let go of the key?

Answer: There could be a problem with the ignition switch. Gain access to the ignition switch and see if the harness connector is getting loose. Push the connector and switch together and try to start the engine and see if it stays running. If so, you may want to use a large plastic tie to secure the connection. Or you may need to replace the switch.

© 2018 Dan Ferrell

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