* Idle Air Control (IAC) Valve: This valve regulates air flow into the engine at idle. If it's dirty, sticking, or failing, the engine might not get enough air when you lift off the gas pedal, causing it to stall. This is a very common cause of this symptom.
* Throttle Position Sensor (TPS): This sensor tells the computer the position of the throttle. A faulty TPS can send incorrect information, leading to improper fuel mixture and stalling, especially when the throttle is transitioning from open to closed.
* Vacuum Leaks: A significant vacuum leak in the intake system can cause erratic idle and stalling. Look for cracked or loose hoses, especially those related to the brake booster, PCV system, and intake manifold.
* Mass Air Flow (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause incorrect fuel delivery, resulting in stalling.
* Fuel Delivery Issues: While less likely to cause stalling *only* when letting off the gas, problems with the fuel pump, fuel filter, or fuel pressure regulator could contribute. If you also experience hesitation or poor acceleration, this is more likely.
* Computer Problems (PCM): In some cases, a faulty PCM (Powertrain Control Module) can cause these symptoms. This is less common, but possible.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Visually inspect all vacuum hoses for cracks, looseness, or damage. Listen for hissing sounds near the intake manifold when the engine is running.
2. Clean the IAC Valve: This is usually a quick and easy fix. Remove the IAC valve, clean it with carburetor cleaner (paying attention to not damage the delicate internal parts), and reinstall it.
3. Check the TPS: You may need a multimeter to test the TPS voltage output. A faulty TPS often needs replacement.
4. Clean the MAF Sensor: Carefully clean the MAF sensor with a MAF sensor cleaner. Do not touch the sensor element with your fingers.
5. Check Fuel Pressure: If you suspect a fuel delivery problem, have the fuel pressure checked by a mechanic.
Important Note: Diagnosing these issues accurately can be tricky and requires some mechanical knowledge or access to diagnostic tools. If you're not comfortable working on your vehicle yourself, take it to a qualified mechanic for diagnosis and repair. Ignoring the problem could lead to further damage.
