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.
See Fuel Delivery and Air Induction


Base idle speed too low See Adjustments


Idle speed control valve
defective or sticking See Fuel Delivery and Air Induction


EGR malfunction See Exhaust Gas Recirculation System


Incorrect distributor installed position Check ignition timing
See Adjustments


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


Plugged or restricted fuel injector(s) See Fuel Delivery and Air Induction


Electronic spark timing See 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 System


PCV system malfunction See Positive Crankcase Ventilation System