Rough Or Unstable Idle

Check for play in throttle cable.
Check for contaminated fuel.
Check for clogged air filter.
Check for vacuum leaks.
Check cooling system.
Check compression.
Check spark plugs.
Check idle speed.
Check fuel pressure.
Check for cracked distributor cap.
Check ignition and valve timing.
Clogged MAP sensor (pressure sensor) vacuum hose (if equipped).
Check for faulty ECM.
Check for faulty air valve (if equipped).
Check for faulty coolant (water) temperature sensor.
Check for faulty air temperature sensor (if equipped).
Check for faulty A/C vacuum switching valve (if equipped).
Check for faulty Idle Speed Control (ISC) solenoid valve (if equipped).
Check for faulty throttle opener system (if equipped).
Check for malfunctioning EGR valve (if equipped).
Check for malfunctioning PCV valve.
Check for malfunctioning electronic fuel injection system.
Check for worn distributor terminals.
Ensure sufficient secondary spark is available.