Why Does My Car Stall When Cold?

Updated on March 31, 2020
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

When bad, there are a few common components that can cause your car to stall when cold.
When bad, there are a few common components that can cause your car to stall when cold. | Source

If your car stalls when cold, you may be dealing with a problem in one or more sensors or components:

  • bad EGR valve
  • faulty coolant temperature sensor
  • bad intake air temperature sensor
  • bad MAP sensor

In the following sections, you'll find different sensors o components that might be causing your engine to stall when cold.

Usually, a faulty sensor will trigger the check engine light on your vehicle. So first scan your car's computer for diagnostic trouble codes (DTCs), even if the engine light is not on. You may find a pending code that can guide you in your diagnostic.

Index
1. Faulty Engine Coolant Temperature Sensor
2. Bad Intake Air Temperature Sensor
3. Faulty Manifold Absolute Pressure Sensor
4. Bad Idle Air Control Valve
VIDEO: Checking an IAC Valve Causing a Cold Stall
5. Faulty EGR Valve
6. Tips for Repairing Your Vehicle at Home
Test the engine coolant temperature sensor if it seems stuck or malfunctioning.
Test the engine coolant temperature sensor if it seems stuck or malfunctioning. | Source

1. Faulty Engine Coolant Temperature Sensor

Sometimes, a bad or stuck engine coolant temperature (ECT) sensor will send the computer the wrong signal. If the computer believes the engine is warm because of a bad signal from the ECT, it will command less fuel than the engine needs to operate during a cold start.

Most of the time, you can check the ECT sensor yourself. This post will help you test the coolant temperature sensor. For this, you'll need a few common tools and a digital multimeter.

A faulty intake air temperatue sensor can disrupte fuel delivery.
A faulty intake air temperatue sensor can disrupte fuel delivery. | Source

2. Bad Intake Air Temperature Sensor

A faulty intake air temperature (IAT) sensor can also upset the air-fuel mixture, just like a bad CTS.

The computer also relies on the IAT sensor to calculate fuel delivery. If the IAT tells the computer the air entering the intake system is warmer than it actually is, the computer will decrease fuel delivery to the engine.

During a cold start, this can cause rough idle and stalling issues.

The IAT sensor is a thermistor that changes resistance with changes in temperature. The higher the temperature, the lower the sensor's resistance.

On some models, the IAT sensor is part of the MAF sensor. On other models, it may be located in the intake air duct. Consult your vehicle repair manual.

Testing an IAT sensor:

The following is a general testing procedure for an IAT sensor using an ohmmeter.

  1. Make sure the engine is cool.

  2. Unplug the IAT sensor electrical connector.

  3. Measure the resistance across the sensor two terminals.

    • at about 86 F (30 C), you may get around 24,000 ohms.
    • at about 68 F (20 C), you may get around 37,000 ohms.
  4. Plug in the IAT sensor electrical connector.

  5. Start and idle the engine until it reaches operating temperature, about 20 minutes.

  6. Shut off the engine.

  7. Unplug the IAT sensor electrical connector.

  8. Measure the resistance across the sensor's two terminals.

    • at about 194 F (90 C), you may get around 2,800 ohms.
    • at about 212 F (100 C), you may get around 2,070 ohms.

Compare your results to the specifications listed in your vehicle repair manual. If resistance values are correct, check the reference voltage from the computer to the sensor.

A faulty MAP sensor may cause the engine to stall when cold on some models.
A faulty MAP sensor may cause the engine to stall when cold on some models. | Source

3. Faulty Manifold Absolute Pressure Sensor

The manifold absolute pressure (MAP) sensor also has an effect on the air-fuel mixture. Among other symptoms, a faulty MAP sensor can also cause your engine to stall when cold.

There are different ways to test a MAP sensor, depending on the recommendation of your car manufacturer and the type of sensor installed in your vehicle.

Different ways to test a map sensor depending on application:

  • Using a vacuum pump and a digital multimeter.
  • Testing for resistance.
  • Testing for voltage at specific terminals.

Consult your vehicle repair manual for the best way to test your MAP sensor.

This other post can help you test your map sensor using a vacuum pump and digital multimeter.

Check the idle air control valve for carbon buildup around passages.
Check the idle air control valve for carbon buildup around passages. | Source

4. Bad Idle Air Control Valve

The car computer uses the idle air control (IAC) valve or solenoid to regulate idle speed. It also uses the valve to control the amount of air needed as fuel is injected into the engine.

Often, a faulty valve will cause the engine to run rough at idle. A common issue is carbon deposits that buildup and lodge around the valve pintle and passages.

But at its early stages, the valve may cause a problem at cold starts in some models. The valve is not difficult to check and you can do it yourself at home with the use of a multimeter.

This other post will help you do a visual inspection of the valve and passages, and test the idle air control valve, if necessary.

The following video shows you how a dirty IAC valve kept a 1999 Toyota Camry from starting when cold. Once the passages and throttle body are cleaned, idle improves.

Checking an IAC Valve Causing a Cold Stall

The EGR valve may stick open and cause the engine to stall.
The EGR valve may stick open and cause the engine to stall. | Source

5. Faulty EGR Valve

On some models, a faulty EGR valve can cause your engine to stall at idle when cold.

Usually, the EGR valve becomes sticky and remains open. If you are able to warm up the engine, the valve may close and function properly afterwards.

Check and test the valve for proper operation. This other post will help you test the EGR valve in your vehicle.

Use your vehicle repair manual to check specs for your own component applications during your tests.
Use your vehicle repair manual to check specs for your own component applications during your tests. | Source

6. Tips for Repairing Your Vehicle at Home

These are the most common sensors that may be causing your engine to stall when cold. But make sure to scan your car's computer for potential DTCs. Troubleshoot any system or components indicated by your DTCs, if any.

If you don't find any trouble codes, check one or more of the sensors listed in this guide.

Often, you'll find the fault in one of them and be able to repair your vehicle yourself using a few common tools. Remember to have the vehicle repair manual for your particular vehicle make and model. The manual gives you the specifications for any component you may need to test, and, if necessary, the correct test procedure for your particular application.

If you don't have this manual yet, you can buy a relatively inexpensive, aftermarket manual at your local auto parts store or through Amazon. Haynes manuals come with step-by-step procedures for many maintenance, troubleshooting, and replacement component projects you can do at home. So you'll be using your manual often, saving time and money in vehicle repairs.

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.

© 2020 Dan Ferrell

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