Rough Unstable Idle

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

POSSIBLE CAUSE ACTION


PCV valve malfunction Check PCV system.

Incorrect Air-Fuel mixture Check fuel pressure.
Check O2 sensor.
Perform injector balance test (MPI).

Faulty canister purge Check Fuel Evaporative System.
Evaporative Emissions System

Restricted exhaust system Check Catalytic Converter.
See Plugged or Restricted Exhaust Testing.

Idle speed too low Perform Minimum Airflow Test.
SEE Powertrain Management/Computers and Control Systems/Testing and Inspection/Procedures.

Dirty air filters Clean or replace

Poor or contaminated fuel Recommend higher grade fuel