Simple & Relatively Easy to Check:
* Vacuum Leaks: A vacuum leak in the intake manifold, vacuum lines, or even a slightly loose connection can disrupt the idle control system. Listen carefully for hissing sounds near the engine when it's idling. Visually inspect all vacuum lines for cracks or disconnections.
* Dirty Throttle Body: A dirty or sticky throttle body will impede airflow and cause a higher than normal idle. Clean it thoroughly with throttle body cleaner, following the instructions carefully.
* Faulty Idle Air Control (IAC) Valve: This valve regulates air flow at idle. A dirty or malfunctioning IAC valve is a common cause of high idle. Cleaning it (similar to the throttle body) is often a first step. If cleaning doesn't solve it, replacement might be necessary.
* Faulty Throttle Position Sensor (TPS): This sensor tells the computer the position of the throttle. A faulty TPS can cause erratic idle and other driveability issues. These often need to be replaced.
* Incorrect Throttle Cable Adjustment: If the throttle cable is too tight, it can keep the throttle plate slightly open, leading to a high idle.
More Complex Issues:
* Problems with the PCM (Powertrain Control Module): The PCM controls many aspects of engine operation. A faulty PCM is less likely but possible. Diagnosing this usually requires a professional scan tool.
* EGR Valve Issues: The Exhaust Gas Recirculation valve can sometimes stick open or malfunction, leading to a high idle.
* Mass Airflow Sensor (MAF) Problems: A faulty MAF sensor can cause inaccurate air readings, leading to a rich fuel mixture and high idle.
* Air Filter Restriction: Though less common as the cause of *high* idle, a severely clogged air filter can restrict airflow forcing the engine to compensate and potentially raise the idle.
Troubleshooting Steps:
1. Check the easy stuff first: Start with the vacuum lines, throttle body, and IAC valve. Cleaning these is often inexpensive and can resolve the problem.
2. Listen for hissing: Pay close attention to any hissing sounds around the intake manifold and vacuum lines which indicate a leak.
3. Use a scan tool (OBD-II): A scan tool can retrieve diagnostic trouble codes (DTCs) which might point to the specific problem. Auto parts stores often offer free code reading services.
4. Check engine oil level: Low engine oil can increase idle in some instances, though not the most common cause.
Important Note: If you're not comfortable working on your vehicle's engine, it's best to take it to a qualified mechanic for diagnosis and repair. Improperly working on your vehicle's engine system could cause further damage.
