* Throttle Position Sensor (TPS): A faulty TPS provides inaccurate readings to the engine control module (ECM), causing incorrect fuel delivery and potentially a high idle. This is a strong suspect given your symptoms.
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor delivers incorrect readings about the amount of air entering the engine. This can lead to a rich or lean fuel mixture, impacting performance and causing high idle. Cleaning the MAF sensor (carefully, with MAF sensor cleaner) is a good first step.
* Idle Air Control (IAC) Valve: This valve regulates airflow at idle. A malfunctioning IAC valve can cause erratic idle speeds, including high idle.
* Vacuum Leaks: Vacuum leaks can disrupt the engine's proper operation, potentially causing high idle and reduced power. Check all vacuum hoses for cracks or disconnections.
* Engine Coolant Temperature Sensor: If the ECM receives a faulty reading from this sensor, it might cause the engine to run at a higher speed.
* ECM Issues: While less likely, a problem with the engine control module itself could cause these symptoms. This is usually diagnosed last after other components are checked.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Inspect all vacuum hoses and connections carefully. A hissing sound near the engine indicates a leak.
2. Clean the MAF Sensor: Use a MAF sensor cleaner and follow the instructions carefully. Don't touch the sensor element with your fingers.
3. Check the TPS: This often requires a multimeter and checking voltage readings according to your Trailblazer's repair manual or online resources specific to your year and engine.
4. Check the IAC Valve: Similar to the TPS, testing this requires a multimeter and checking specifications.
5. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any codes stored in the ECM. These codes can pinpoint the problem. Auto parts stores usually offer free code reading services.
Important Notes:
* Safety First: Always disconnect the negative battery terminal before working on any electrical components.
* Repair Manual: A repair manual specific to your 2002 Trailblazer V6 will be invaluable for detailed instructions and specifications. You can find them online or at auto parts stores.
* Professional Help: If you're not comfortable performing these checks or repairs yourself, take your Trailblazer to a qualified mechanic. Continuing to drive it with these problems could cause further damage.
The high-pitched sound might be related to the high idle, but it could also indicate a separate issue like a belt or pulley problem. Thoroughly investigate the above potential causes to find the root of the problem.
