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
^ ENGINE SPEED/REFERENCE SENSOR: Check for improperly positioned or damaged sensor. Check for damaged or missing teeth at the reference wheel. Refer to Crankshaft Position Sensor, Testing and Inspection

^ 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 Digital Motor Electronic (DME) control unit will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
^ THROTTLE POSITION SWITCH/SENSOR: Improper adjustment. Refer to Throttle Position Sensor, Adjustments

^ COOLANT TEMPERATURE SENSOR: Refer to Coolant Temperature Sensor, Coolant Temperature Sensor/Switch (For Computer)



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, Testing and Inspection



IGNITION
^ SECONDARY IGNITION SYSTEM: Refer to Ignition Systems, Testing and Inspection

^ DME CONTROL UNIT: DME final output stages.



EMISSIONS
^ EVAPORATIVE SYSTEM: Test purge valve and charcoal canister operation.
^ PCV VALVE: Test for proper operation.

Positive Crankcase Ventilation



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.
^ A/C refrigerant pressure too high, overcharge or faulty high pressure switch.
^ MOTOR MOUNTS:
^ CYLINDER COMPRESSION: