Here's a breakdown of why and what to do:
* Idle Air Control (IAC) Valve: This valve regulates the amount of air entering the engine at idle. A faulty IAC valve can cause a high idle because it's letting in too much air.
* Throttle Position Sensor (TPS): This sensor tells the computer the position of the throttle. A faulty TPS can send incorrect signals, leading to an incorrect idle speed.
* Vacuum Leak: A leak in the intake system can cause the engine to take in more air than expected, resulting in a high idle. This is often harder to pinpoint.
* Mass Airflow Sensor (MAF Sensor): While less likely to cause *only* a high idle, a dirty or faulty MAF sensor can provide inaccurate readings of air intake, potentially leading to an incorrect fuel mixture and affecting idle.
What you should do:
1. Get the Diagnostic Trouble Codes (DTCs): The best first step is to get the DTCs from your vehicle's onboard diagnostic system (OBD-II). You can do this with a relatively inexpensive OBD-II scanner from an auto parts store. The codes will give you a much better idea of the specific problem.
2. Check for Vacuum Leaks: Visually inspect all vacuum hoses and connections for cracks, splits, or loose fittings. Pay close attention to the area around the intake manifold. A shop vac can sometimes help find a leak by listening for the hissing sound as you test various areas.
3. Clean the MAF Sensor (carefully): If you have a MAF sensor cleaner, carefully clean the sensor element (following the instructions on the cleaner – don't touch the sensor element itself). A dirty MAF sensor can cause performance issues.
4. Professional Diagnosis: If you can't find any obvious vacuum leaks and the DTCs don't point to an obvious solution (or you're uncomfortable working on your car), take it to a mechanic. They have the tools and expertise to diagnose the problem accurately.
Important Note: Continuing to drive the vehicle with a high idle can cause further damage. It's best to address the problem as soon as possible. The high idle itself might be a symptom of something more serious.
