* Fast Idle Cam: The most likely culprit is a malfunctioning fast idle cam or its related components. This mechanism is designed to increase idle speed when the engine is cold to help it warm up more quickly. If it's sticking, damaged, or improperly adjusted, it can cause a persistently high idle even after the engine warms up.
* Throttle Position Sensor (TPS): A faulty TPS can provide incorrect information to the engine computer (ECM), leading to an elevated idle. The ECM might try to compensate for what it *thinks* is a low throttle position, resulting in a high idle.
* Mass Airflow Sensor (MAF) Sensor: Similar to the TPS, a dirty or malfunctioning MAF sensor can provide inaccurate air flow readings, causing the ECM to adjust the fuel mixture improperly and lead to a high idle.
* Vacuum Leaks: Leaks in the vacuum system can cause erratic idle speeds, including a high idle. Check all vacuum hoses and connections for cracks, splits, or loose fittings. A particularly significant leak can cause this problem.
* IAC (Idle Air Control) Valve: The IAC valve regulates airflow at idle. A dirty or sticking IAC valve can prevent the engine from properly idling at the correct speed.
* Coolant Temperature Sensor (CTS): If the CTS is faulty and reading a falsely low coolant temperature, the ECM will think the engine is still cold and maintain a higher idle speed.
* Engine Coolant: If your engine is low on coolant this could lead to the CTS reading an inaccurate temperature and causing a high idle to maintain a higher operating temperature. Check your coolant level.
Troubleshooting Steps:
1. Check for Vacuum Leaks: This is the easiest and quickest check. Visually inspect all vacuum hoses and connections.
2. Clean the IAC Valve: This is often a simple fix. Remove the IAC valve, clean it with throttle body cleaner, and reinstall it.
3. Check the Coolant Temperature Sensor: Use a multimeter to test the CTS resistance values at different temperatures to see if they are within the specifications listed in your vehicle's repair manual.
4. Check the TPS and MAF Sensor: These sensors are more difficult to diagnose and often require specialized tools or a scan tool to accurately test. You may need a professional mechanic for this step.
5. Inspect the Fast Idle Cam: This is more involved and often requires a repair manual to understand how it works and how to adjust or repair it.
Important Note: Before attempting any repairs, it's crucial to consult a repair manual specific to your 1995-2005 Chevy Lumina Z34 3.4L. This will provide detailed diagrams, specifications, and procedures. If you're not comfortable working on your vehicle, it's best to take it to a qualified mechanic for diagnosis and repair.
