Rough, Unstable Or Incorrect Idle
If engine runs unevenly at idle (may shake) or if idle speed is incorrect or unstable (RPM varies, engine is hunting), check the following items:
- Ensure no vacuum leaks exist.
- Check PCV valve operation.
- 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 correctly and not leaking.
- Clean fuel injectors.
- Check for fuel in vacuum hose to fuel pressure regulator.
- Check for low compression.
- Check for broken motor mounts.
- Determine if condition is caused by a rich or lean system. Using Tech 1, measure O2S/HO2S output voltage while driving vehicle when condition exists. Voltage less than .45 volt, indicates a lean system. Voltage greater than .45 volt, indicates a rich system.
- Check O2S/HO2S operation and for RTV sealant or silicone contamination. Also check for sensor cracking or glycol contamination. This will cause a false high voltage signal to ECM. ECM will respond by reducing (leaner) air/fuel ratio.
- Check EGR and solenoid operation (There should be no EGR operation at idle).
- Check air valve, IAC or ISC valve operation.
- Check MAP sensor operation.
- Check TP sensor for a sticking throttle shaft or binding throttle linkage.
- Check charging system output. Repair charging system if voltage is not 12-16 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 overcharged, pressure to high or faulty dual pressure switch.
- Check Engine Coolant Temperature (ECT) sensor.
- Check Mass Airflow (MAF) sensor.