Stalls/Rough, Unstable or Incorrect Idle

SYMPTOM DESCRIPTION:
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 severe enough to cause stalling. Engine idles at incorrect speed. Check the following systems and components.



COMPUTER INPUTS/OUTPUTS

^ IDLE VALVE:
^ AIR FLOW METER:
^ OXYGEN SENSOR (O2) - Inspect sensor for silicon contamination from fuel, or use of improper RTV sealant. The sensor will have a white, powdery coating, and will result in a high but false signal voltage (rich exhaust indication). The electronic fuel injection(EFI) control unit will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
^ THROTTLE POSITION SWITCH/SENSOR:
^ COOLANT TEMPERATURE SENSOR:



FUEL
^ FUEL INJECTOR BALANCE TEST: Poor spray pattern, clogged or stuck.
^ FUEL PRESSURE: Check fuel pressure and output volume.
Refer to Fuel Delivery and Air Induction,



IGNITION
^ SECONDARY IGNITION SYSTEM.




EMISSIONS
^ EVAPORATIVE SYSTEM: Purge valve and charcoal canister operation.




ENGINE
^ VACUUM LEAKS: Test for vacuum leaks at intake system.
^ BATTERY: Cables and ground straps should be clean and secure.
^ CRANKCASE AIR LEAKS: Check at dip stick seal, oil filler cap, front and rear engine oil seals.
^ MOTOR MOUNTS:
^ CYLINDER COMPRESSION: