For 1990-2009 cars

Checks | Actions
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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.
Misfire Counts | Check misfire counts using a scan tool (if any exist)
Throttle Linkage | Check throttle linkage for sticking or binding
Throttle Position Sensor | Check throttle position sensor, should read 0% at idle on a scan tool.
Idle Air Control (IAC) Valve | Check for a carboned-up IAC valve .
Generator charging output voltage | Repair if less than 13 volts or more than 16 volts with engine running and all accessories OFF.
Injectors | Check for clogged injectors. Perform Injector Balance test.
Evaporative Emissions (EVAP) solenoid | Check for EVAP purge solenoid stuck open.
Catalytic Converter | Check for Catalytic converter blockage.
Engine Mounts | Broken or loose engine mounts
Fuel | Check fuel quality
DTC P1599 | Check DTC P1599 -- refer to chart.
Exhaust Gas Recirculation (EGR) Valve | Check for EGR valve stuck open.
Electronic Ignition (EI) | Check terminals and wires at EI module.
Powertrain Control Module (PCM) | Check PCM power and grounds.
Vacuum leak | Check for vacuum leak.
Fuel pressure | Check fuel pressure.
Spark plugs and Wires | Check park plugs and wires for arcing or corrosion.
Cylinder Compression | Check cylinder compression.
Long term fuel trim values | Monitor long term fuel trim values on a scan tool to check if system is running rich or lean.