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:

• Perform VISUAL/PHYSICAL INSPECTION  .
• Ensure no vacuum leaks exist.
• Check PCV valve operation.
• Ensure PCM ground connections are clean, tight and routed properly.
• Ensure base idle speed 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 condition. Using scan tool, 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 PCM. PCM will respond by reducing (leaner) air/fuel ratio.
• Check EGR and solenoid operation.
• Check air valve, Idle Air Control (IAC) or Idle Speed Control (ISC) valve operation.
• Check Manifold Absolute Pressure (MAP) sensor operation.
• Check Throttle Position (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 PCM application. Check with dealer for latest PCM application.
• Check canister purge and PCV valve operation.
• Check for A/C signal to PCM when A/C is on.
• Check park/neutral switch operation.
• A/C system overcharged, pressure too high or faulty dual pressure switch.
• Check Engine Coolant Temperature (ECT) sensor.