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 Delivery and Air Induction.


Base idle speed too low See Adjustments.


Idle speed control valve Refer to Computers and
defective or sticking Control Systems.


Incorrect distributor installed position Check ignition timing
See Adjustments.


Fouled spark plugs, defective ignition wires Inspect spark plugs and wires.
Refer to Ignition System.


Plugged or restricted fuel injector(s) Refer to Fuel Delivery and Air Induction.


Electronic spark timing
insufficient spark advance Refer to Computers and Control Systems.


Restricted exhaust See Three Way Catalytic Converter


Poor or contaminated fuel Recommend higher quality fuel


EVAP system malfunction See Evaporative Emission Control Systemm


PCV system malfunction See Positive Crankcase Control System