Simple/Easy Checks:
* Throttle Body: A dirty or sticky throttle body can prevent it from closing completely, leading to a high idle. Cleaning it with throttle body cleaner is often a quick and effective solution.
* Vacuum Leaks: Small holes or cracks in vacuum lines can disrupt the engine's air-fuel mixture, causing a higher idle. Inspect all vacuum lines visually for damage.
* IAC (Idle Air Control) Valve: This valve regulates air flow at idle. A malfunctioning IAC valve can cause erratic idle speeds, including high idle. Cleaning it might help, but replacement is often necessary if cleaning doesn't resolve the issue.
* MAF (Mass Airflow) Sensor: A dirty or faulty MAF sensor provides inaccurate readings to the engine computer, which can lead to an incorrect air-fuel mixture and a high idle. Cleaning the sensor (carefully!) might help; replacement is often necessary if cleaning fails.
More Complex Issues:
* Faulty Engine Control Module (ECM): The ECM controls many engine functions, including idle speed. A malfunctioning ECM can cause a variety of problems, including a high idle. This requires professional diagnosis and replacement.
* Problem with the Air Intake System: A restriction in the air intake system (e.g., a clogged air filter) can cause the engine to compensate by increasing the idle speed. Check and replace the air filter if necessary.
* Throttle Position Sensor (TPS): A faulty TPS sends incorrect information to the ECM about the throttle position, potentially leading to a high idle.
* PCV (Positive Crankcase Ventilation) Valve: A clogged or faulty PCV valve can cause excessive pressure in the crankcase, which can affect the idle.
* Vacuum leaks in the intake manifold: More serious than smaller vacuum leaks; these can significantly disrupt the engine's operation.
Troubleshooting Steps:
1. Check the obvious: Start with the easy checks: clean the throttle body, inspect vacuum lines, and replace the air filter.
2. Use an OBD-II scanner: This will provide diagnostic trouble codes (DTCs) that can pinpoint the problem. Auto parts stores often offer free OBD-II scans.
3. Consult a repair manual: A repair manual specific to your Impala's year and model will provide detailed information on diagnosing and repairing engine problems.
4. Seek professional help: If you're not comfortable working on your car yourself, or if you've tried the simple fixes and the problem persists, take it to a qualified mechanic for diagnosis and repair.
Important Note: The specific cause of a high idle will depend on the year, make, and model of your Impala. Providing the year of your Impala would help narrow down the possibilities.
