- Idle Air Control (IAC) valve: The IAC valve controls the amount of air that bypasses the throttle body when the engine is idling. If the IAC valve is faulty, it can cause the engine to stall when put in gear.
- Throttle Position Sensor (TPS): The TPS is a sensor that monitors the position of the throttle plate. If the TPS is faulty, it can cause the engine to stall when put in gear.
- Fuel pressure: Insufficient fuel pressure can cause engine stalling.
- Vacuum leaks: Vacuum leaks can cause the engine to stall by leaning out the air/fuel mixture.
- Transmission fluid: Check your transmission fluid levels as low fluid may also be a cause of stalling in gear.
- Dirty throttle body: A dirty throttle body can impede airflow and cause stalling in gear.
Troubleshooting:
1. Check the IAC valve: First, check the condition of the IAC valve. It should be clean and free of debris. If the IAC valve is dirty, clean it with a throttle body cleaner.
2. Check the IAC valve operation: You can check the operation of the IAC valve by disconnecting it from the electrical connector. If the engine speed increases when the IAC valve is disconnected, then the IAC valve is likely faulty.
3. Check the TPS: Inspect the TPS for damage. You can check the operation of the TPS by moving the throttle plate and watching the output voltage of the TPS change smoothly and proportionally. If the output voltage of the TPS does not change smoothly, or if it does not reach the specified values, then the TPS may be faulty.
4. Check the fuel pressure: Check the fuel pressure with a fuel pressure gauge. If the fuel pressure is low, then it could be causing the engine to stall.
5. Check for vacuum leaks: Inspect all the vacuum hoses for leaks. You can use a smoke machine to find vacuum leaks. If there is a vacuum leak, repair it and see if this resolves the stalling issue.
6. Check the transmission fluid level: Ensure the transmission fluid is filled to the proper level. If it's low, add transmission fluid and see if that resolves the issue.
7. Clean the throttle body: Remove the throttle body from the engine and clean it with a throttle body cleaner. If it's excessively dirty, you may need to soak the throttle body in cleaner overnight. Reinstall the cleaned throttle body and see if starting in gear is possible.
If none of these solutions resolve the problem, you should take your vehicle to a qualified mechanic for further diagnosis.
