Rough, Unstable, or Incorrect Idle and Stalling

DEFINITION: The engine runs unevenly at idle. If bad enough, the vehicle may shake. Also, the idle may vary in RPM (called hunting). Either condition may be had enough to cause stalling. Engine idles at incorrect speed:

Check:
^ Misfire counts using Scan tool (if any exist)
^ APP AT IDLE should read YES on Scan tool with no pedal input.
^ Generator charging output voltage. Repair if less than 13 volts or more than 16 volts with engine running and all accessories Off.
^ Injectors clogged. Perform Injector Balance test. Component Tests and General Diagnostics
^ EVAP purge solenoid stuck open
^ Catalytic converter blockage
^ Fuel quality
^ Broken or loose engine mounts
^ Check terminals and wires at EI module
^ ECM power and grounds
^ Vacuum leak (intake leak between MAF sensor and throttle body)
^ Fuel pressure
^ Spark plugs and boots for corrosion/arcing
^ Cylinder compression

Monitor long term fuel trim values on Scan tool if system is running rich or lean.