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.