Car stalls when it warms up

Hi and thanks for using 2CarPros.

Does the engine start right back up, or do you have to wait for awhile before it restarts? Also, here is a link that discusses engine stall at idle. I am adding it because there may be something helpful in it for you.

https://www.2carpros.com/articles/stall-at-idle

Also, often times when a crankshaft position sensor is going bad, it will shut the engine down when it warms up, but once it cools, the engine will restart. Here is a link that discusses symptoms of a bad sensor:

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

I am adding that because I do not know if it restarts right away.

Let me know if anything here helps or if you have other questions.

Take care,
Joe

Welcome back.

Okay, it could be a few things. Before anything, see if the engine idle speed is at least between 700 and 800 rpm's at idle. If it is low, you can adjust it up (see below / Last resort). However, If the engine stalls or the engine speed is low, it is probable that deposits are adhered to the throttle valve, so clean it.

https://www.2carpros.com/articles/throttle-actuator-service

Next, if the engine restarts, chances are it is either a engine vacuum leak, a bad coolant temp sensor, a bad idle air control valve, a crank sensor, and so on. Now, is the check engine light staying on when the engine is running? If so, you should scan it.

https://youtu.be/YV3TRZwer8k

If there are no codes, the next suggestion would be to check for a vacuum leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If that all checks good, the idle air control valve needs checked.

Here are directions for testing the idle air control valve. It is responsible for maintaining engine idle speed. The directions are extensive and require use of a multi-meter and basic understanding of testing wiring. Before performing the test, remove the IAC, located on the throttle body (see pic 1) and make sure there isn't dirt or corrosion on the portion that goes into the throttle body or in the throttle body where it mounts. If there is, clean and reinstall and test.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

Testing (see pics 2-4)
IDLE AIR CONTROL MOTOR (STEPPER MOTOR) CHECK

Required Special Tool:
- MB991709: Test Harness Set

Checking the Operation Sound
1. Check that the engine coolant temperature is 20 °C (68 °F) or below.

NOTE: If necessary, you can disconnect the engine coolant temperature sensor connector and connect the harness-side of the connector to another engine coolant temperature sensor that is at 20 °C (68 °F) or below.

2. Check that the operation sound of the stepper motor can be heard after the ignition is switched ON (but do not start the engine).
3. If the operation sound cannot be heard, check the stepper motor's activation circuit. If the circuit is normal, it is probable that there is a malfunction of the stepper motor or engine control module (ECM) or powertrain control module (PCM) .

Checking the Coil Resistance
1. Disconnect the idle air control motor connector.

2. Measure resistance between terminal No. 2 and either terminal No. 1 or terminal No. 3 of the connector at the idle air control motor side.

Standard value: 28 - 33 Ohms [at 20 °C (68 °F)]

3. If resistance is not within the standard value, replace the IAC motor.
4. Measure the resistance between terminal No. 5 and either terminal No. 6 or terminal No. 4 of the connector at the idle air control motor side.

Standard value: 28 - 33 Ohms [at 20 °C (68 °F)]

5. If resistance is not within the standard value, replace the IAC motor.

1. Remove the throttle body.
2. Remove the idle air control motor.
3. Connect special tool MB991709 to the idle air control motor connector.

4. Connect the positive (+) terminal of a power supply (approximately 6 volts) to terminal No. 2 and the terminal No. 5.
5. Connect the negative (-) terminal of the power supply to each clip as described in the following steps. Then check whether or not the stepper motor vibrates slightly as it operates.
1). Connect the negative terminal of the power supply to terminal No. 1 and terminal No. 4.
2). Connect the negative terminal of the power supply to terminal No. 3 and terminal No. 4.
3). Connect the negative terminal of the power supply to terminal No. 3 and terminal No. 6.
4). Connect the negative terminal of the power supply to terminal No. 1 and terminal No. 6.
5). Connect the negative terminal of the power supply to terminal No. 1 and terminal No. 4.
6). Repeat the tests in sequence from (5) to (1) to test opposite movement of the IAC.
6.

If vibration is detected during the test, the stepper motor can be considered to be normal.

If it is clean and the idle air control valve (IAC) is clean and working and no other problems are found, here is where idle speed is adjusted. Only do this as a last resort. See pic 5

Okay, you indicated little knowledge in the heading. Please feel free to ask questions that you have. I realize this may be intimidating.

Take care,
Joe