Rough, Unstable Or Incorrect Idle
If engine runs unevenly at idle or if idle speed is incorrect or unstable, check the following items:
- Ensure no vacuum leaks exist.
- Check ECM ground connections.
- Ensure base idle adjustment is correct.
- Verify vacuum hose routing is correct.
- Check for defective ignition system components.
- Ensure ignition timing and controls are working properly.
- Ensure all fuel injectors are operating.
- Clean fuel injectors.
- Check for fuel in vacuum hose to fuel pressure regulator.
- Check for low compression.
- Check for damaged basic engine parts such as camshaft, valves etc.
- Check O2 sensor operation or for RTV sealant contamination. This will cause a false high voltage signal to ECM. The ECM will respond by reducing (leaner) air/fuel ratio.
- Check EGR and solenoid operation.
- Check air valve, IAC or ISC valve operation.
- Check MAP sensor operation.
- Ensure throttle linkage is not binding.
- Check charging system output. Repair charging system if voltage is not between 9 and 16 volts.
- Ensure correct ECM application. Check with dealer for latest application information.
- Check canister purge and PCV valve operation.
- Check for A/C signal to ECM when A/C is on.
- Check park/neutral switch operation.
- A/C system pressure too high.
- Check coolant temperature sensor.
- Check mass airflow sensor.