Rough Unstable Idle

The engine runs unevenly. In severe cases, the car may actually shake. The engine idle may hunt or fluctuate in rpm and may be bad enough to stall.

POSSIBLE CAUSE ACTION

Unmeasured air (vacuum leak) Check air flow meter,
intake air ducts, manifold,
and vacuum components.
Refer to FUEL SYSTEMS.


Base idle speed too low See ADJUSTMENT PROCEDURES.


Idle speed control valve Refer to COMPUTERIZED ENGINE
defective or sticking CONTROLS.


Incorrect distributor installed position Check ignition timing
See ADJUSTMENT PROCEDURES.


Fouled spark plugs, defective ignition wires Inspect spark plugs and wires.
Refer to IGNITION SYSTEMS.


Plugged or restricted fuel injector(s) Refer to FUEL SYSTEMS.


Electronic spark timing
insufficient spark advance Refer to COMPUTERIZED ENGINE CONTROLS.


Restricted exhaust Check catalytic converter.


Poor or contaminated fuel Recommend higher quality fuel


EVAP system malfunction Check evaporative emission system.


PCV system malfunction Check PCV system.