1. Idle Air Control (IAC) Valve:
* What it does: The IAC valve regulates the amount of air entering the engine at idle.
* How it might be causing the problem: A dirty or malfunctioning IAC valve can prevent it from closing properly, allowing too much air into the engine and increasing the idle speed.
* Troubleshooting:
* Inspect the valve: Make sure it's clean and free of debris. You can use a spray cleaner for electrical contacts.
* Test the valve: Disconnect the electrical connector and see if the idle speed changes. If it does, the valve may be faulty.
* Replace if necessary: If cleaning doesn't resolve the issue, the valve likely needs replacement.
2. Vacuum Leaks:
* What they are: Cracks or holes in vacuum hoses, intake manifold gaskets, or other vacuum-related components.
* How they cause the problem: A vacuum leak can disrupt the airflow to the engine, leading to an increased idle speed.
* Troubleshooting:
* Inspect hoses: Visually inspect all vacuum hoses for cracks, splits, or loose connections.
* Use a vacuum gauge: Connect a vacuum gauge to the intake manifold and observe the reading at idle. A low reading indicates a leak.
* Spray brake cleaner: Carefully spray around suspected leak areas while the engine is running. If the idle speed changes, you've found the leak.
3. Throttle Position Sensor (TPS):
* What it does: The TPS sends information to the computer about the throttle position, which helps regulate engine speed.
* How it might be causing the problem: A faulty TPS can provide incorrect signals to the computer, causing it to increase the idle speed.
* Troubleshooting:
* Inspect the sensor: Make sure the TPS is clean and connected properly.
* Test the sensor: You can use a multimeter to check the resistance values of the TPS. Consult a service manual for specific values.
* Replace if necessary: If the sensor is faulty, it will need to be replaced.
4. Computer Issues:
* What it does: The engine control module (ECM) manages many engine functions, including idle speed.
* How it might be causing the problem: A faulty ECM or programming issues could cause the idle speed to be set too high.
* Troubleshooting:
* Have the ECM scanned: Use an OBD-II scanner to check for any fault codes related to the engine control system.
* Consult a mechanic: If the ECM is suspected, it's best to have it diagnosed by a qualified technician.
5. Other Potential Causes:
* Faulty air filter: A clogged air filter can restrict airflow, causing the engine to compensate by running at a higher idle.
* Over-advanced ignition timing: Improper ignition timing can also affect idle speed.
* Mechanical issues: Worn engine components like valve guides or piston rings could cause excessive air intake and increased idle speed.
General Tips:
* Check the owner's manual: Your Cavalier's manual should provide specific specifications for the correct idle speed.
* Warm the engine: The idle speed may be higher when the engine is cold and should stabilize once it reaches operating temperature.
* Drive safely: If you're unsure about the cause, drive the car cautiously and avoid high-speed driving until the issue is resolved.
Remember: Diagnosing and fixing car issues can be complex. If you're not comfortable working on your car, it's always best to consult a qualified mechanic.
