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.