* Faulty Idle Air Control (IAC) Valve: This is the most likely culprit. The IAC valve regulates the amount of air entering the engine at idle. If it's stuck open or malfunctioning, it'll allow too much air, resulting in a high idle speed.
* Vacuum Leaks: A leak in the intake manifold, vacuum hoses, or other parts of the vacuum system can cause a lean condition that the engine compensates for by raising the idle speed. Listen carefully around the engine for hissing sounds.
* Throttle Position Sensor (TPS) Issues: A faulty TPS can send inaccurate signals to the engine control unit (ECU), leading to an incorrect idle speed.
* Mass Airflow Sensor (MAF) Problems: A dirty or faulty MAF sensor can also lead to incorrect fuel/air mixture calculations, resulting in a high idle.
* Dirty Throttle Body: A clogged throttle body can restrict airflow, causing the ECU to compensate with a higher idle.
* Engine Coolant Temperature (ECT) Sensor Malfunction: Though less likely to cause a *persistently* high idle, a faulty ECT sensor providing inaccurate temperature readings *could* influence the ECU to maintain a higher idle, especially if the sensor falsely registers a cold engine.
* Faulty PCV Valve: A clogged PCV valve can affect vacuum pressure and cause a high idle.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Visually inspect all vacuum hoses for cracks, splits, or loose connections. Use a propane torch (with the engine running) to carefully check for hissing sounds near suspected leak areas. The hissing will become more pronounced as the propane is near the leak. (Caution: Use extreme care with an open flame near the engine).
2. Clean the Throttle Body: Carefully clean the throttle body using throttle body cleaner. Follow the instructions on the cleaner carefully.
3. Inspect the IAC Valve: Visually inspect the IAC valve for any signs of damage or debris. Sometimes, a gentle cleaning might help, but replacement is often necessary.
4. Check the TPS and MAF Sensor: Have these sensors tested using a multimeter or a scan tool. These tests require some knowledge of automotive electronics. A mechanic can do this easily.
5. ECT Sensor Check: This is less likely but worth checking with a scan tool or multimeter.
6. PCV Valve Inspection: Check the PCV valve for proper operation and replace if necessary.
If you're not comfortable performing these checks yourself, take your Skylark to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and make the necessary repairs. A simple scan tool reading can often quickly pinpoint the culprit.
