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 bad enough to cause stalling. Engine idles at incorrect speed.

Check:
^ Misfire counts using Scan tool (if any exist)
^ Throttle linkage for sticking or binding
^ Throttle position sensor should read 0% percent at idle on Scan tool
^ Idle air control (IAC) valve excessive carbon build-up or deposits
^ 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
^ For DTC P1599 - refer to chart P1599
^ Check terminals and wires at EI module
^ PCM power and grounds
^ Vacuum leak
^ Fuel pressure
^ Spark plugs and boots for corrosion
^ Cylinder compression

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