Rough/Unstable Idle or Stalls

SYMPTOM
The engine runs unevenly at idle. If bad enough, the car may shake. Also, the idle may vary in RPM (called "hunting"). Either condition may be severe enough to cause stalling.

Note: This symptom may be caused by an accumulation of intake valve deposits and/or clogged fuel injectors.

CAUSE (BY SYSTEM/COMPONENT)

IGNITION SYSTEMS
- Ignition timing.


FUEL SYSTEMS
- Injector balance.
- Idle Speed Control.
- Throttle position sensor.
- Air flow sensor.
- Oxygen sensor.

EMISSION SYSTEMS
- EGR "ON" while idling will cause roughness, stalling, and hard starting.
- Check PCV valve for proper operation.
- Perform the usual checks for obvious problems (vacuum leaks, vacuum and electrical circuits correctly connected arcing at distributor or plug wires etc.)

STARTING AND CHARGING SYSTEMS
- Battery cables and ground straps should be clean and secure.

COMPUTERIZED ENGINE CONTROLS
- Power Steering load sensor.