Rough Or Unstable Idle

Check temperature sensor operation.
Check Manifold Absolute Pressure (MAP) sensor (if equipped).
Check for proper CO setting (if adjustable) on mass airflow sensor. Inspect for broken mass airflow sensor filament (if equipped). Check mass airflow sensor continuity.
Inspect induction system. Inspect for vacuum leaks downstream of throttle valve. Inspect duct between mass airflow sensor and throttle body (if equipped).
Check idle speed and EGR valve (if equipped).
Check injector operation and opening duration. Inspect injectors for leaks.
Ensure fuel pump is okay. Check fuel pressure and pressure regulator. Inspect for leaks in fuel lines or restrictions in return line.
Ensure electrical harness, connectors, and wires are not broken or loose. Check all input signals to ECM.
Check EGR valve (if equipped) for proper operation.
Check oxygen sensor.