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


AT ALL TIMES
EGR malfunction, Check EGR system. Refer to TESTING PROCEDURES.
Flange gasket leaking,
valve open (valve should
be closed at idle)



Air management valves Check Air Injection. Refer to TESTING PROCEDURES.
malfunctioning, no
air to ports while
in closed loop



PCV valve malfunction Check PCV system. Refer to TESTING PROCEDURES.



AT OPERATING TEMPERATURE
Faulty canister purge Check Evaporative System. Refer to TESTING PROCEDURES.



Restricted exhaust system Check Catalytic Converter. Refer to TESTING PROCEDURES.




Idle speed too low Check idle load compensator devices in COMPUTERS AND CONTROL SYSTEMS and idle speed in ADJUSTMENT PROCEDURES.