Rough, Unstable Or Incorrect Idle

Engine may stall or vehicle may shake, if engine idle speed is incorrect, varies or is uneven. Check the following items:

• Ensure base idle adjustment is correct.
• Use stethoscope to verify operational noise coming from fuel injector(s).
• Use Spark Tester (ST-125) to ensure sufficient secondary spark is available.
• Check air intake system for restrictions.
• Ensure there are no vacuum leaks.
• Ensure fuel system pressure and volume are correct.
• Verify vacuum hose routing is correct.
• Check for EGR system malfunction.
• Check air valve or ISC valve for malfunction.
• Check power steering pressure switch circuit.
• Check operation of coolant temperature sensor.
• Check electrical connections at throttle body.
• Check for cracks or poor connections at airflow meter or throttle body.
• Check O2 sensor for fluctuating voltage output (0-1.0 volt) with engine at 2000 RPM.
• Verify throttle position sensor has correct adjustment and resistance value.
• Ensure throttle linkage and/or TPS are not sticking or binding.
• If rough idle occurs only when engine is hot, check PCV valve, evaporative emission control system, spark plug gap and compression.