* Idle Air Control (IAC) Valve: This is a common cause. The IAC valve controls the amount of air entering the engine at idle. If it's sticking open or malfunctioning, it'll cause the engine to idle high. Cleaning it is often the first step in troubleshooting.
* Throttle Position Sensor (TPS): A faulty TPS can send incorrect signals to the engine computer (PCM), leading to a high idle. It might need cleaning or replacement.
* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause inaccurate readings, resulting in a high idle. Cleaning it (carefully!) is often the first step.
* Vacuum Leaks: Leaks in the vacuum system can cause the engine to run lean and rev higher. Inspect all vacuum hoses and connections for cracks or loose fittings.
* Engine Coolant Temperature Sensor (ECT): If this sensor is malfunctioning, it could provide incorrect temperature readings to the PCM, causing it to adjust the idle improperly.
* PCM Issues: While less likely, a problem with the Powertrain Control Module (PCM) itself could be responsible. This is usually a last resort diagnosis after checking everything else.
* Throttle Body: A dirty or sticky throttle body can also contribute to high idle. Cleaning it is often beneficial.
Troubleshooting Steps:
1. Check for vacuum leaks: Listen carefully around the engine bay for any hissing sounds that indicate a leak. Visually inspect all vacuum hoses and connections.
2. Clean the IAC, TPS, and MAF sensors: There are many tutorials available online showing how to safely clean these sensors with appropriate cleaner. Do not use harsh chemicals.
3. Check the engine coolant temperature: Make sure the engine is properly cooling. A consistently overheating engine can lead to strange idling behavior.
4. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any trouble codes stored in the PCM. This can provide valuable clues about the problem.
If you're not comfortable working on your car yourself, take it to a qualified mechanic. They have the tools and expertise to diagnose and repair the problem correctly. Trying to fix this without proper knowledge could cause further damage.
