* Idle Air Control (IAC) Valve: This is the most probable cause. The IAC valve regulates air flow at idle. If it's dirty, sticking, or failing, it can cause erratic idle speeds, stalling, and poor fuel economy. Cleaning it (with proper cleaner) is the first thing to try. Replacement is relatively inexpensive.
* Throttle Position Sensor (TPS): A faulty TPS provides inaccurate information to the engine computer (ECU) about the throttle position. This can lead to incorrect fuel delivery and idle control issues, exactly what you're describing. A faulty TPS can cause a rough idle, stalling, and poor MPG.
* Mass Airflow Sensor (MAF) Sensor: The MAF sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor will send incorrect data to the ECU, resulting in a rich or lean fuel mixture, causing the symptoms you're experiencing. Cleaning it (carefully, following instructions specific to your sensor) is worth a try, but replacement might be needed.
* Vacuum Leaks: Vacuum leaks disrupt the engine's carefully balanced air/fuel mixture. Check all vacuum hoses for cracks, leaks, or disconnections. Even a small leak can significantly affect the idle and fuel economy.
* Fuel Pressure Regulator: A faulty fuel pressure regulator might be delivering inconsistent fuel pressure. This can affect idle stability and fuel efficiency.
* Computer (ECU): While less likely, a failing ECU can cause erratic engine behavior. This is usually diagnosed last, after other components have been checked.
* Transmission Issues (if stalling in gear): If the car stalls specifically when engaging a gear, there might be a transmission problem contributing to the stalling. This would require a transmission specialist to diagnose.
Troubleshooting Steps:
1. Check for vacuum leaks: Visually inspect all vacuum lines. Use a vacuum gauge if you have one for a more precise check.
2. Clean the IAC valve: This is the easiest and cheapest thing to try first. Look up a tutorial for your specific car model.
3. Check the TPS voltage: This requires a multimeter. Consult your service manual for the correct voltage readings.
4. Clean the MAF sensor: Again, look up a tutorial specific to your sensor type, as they're delicate.
5. Check fuel pressure: This requires a fuel pressure gauge and might need a mechanic.
Important Considerations:
* Service Manual: Get a service manual specific to your 1992 Mitsubishi Stealth ES. It will provide detailed information on diagnostics and component locations.
* Professional Diagnosis: If you're not comfortable working on your car yourself, take it to a qualified mechanic specializing in Japanese cars. The problem could be a combination of issues.
Don't ignore the issue. Continuing to drive with these symptoms could cause further damage. Start with the simplest checks (vacuum leaks, IAC valve cleaning) and work your way through the more complex ones.
