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


AT ALL TIMES
EGR malfunction, 1. Check the EGR system under TESTING
Flange gasket leaking, PROCEDURES. If OK, step 2
valve open (valve should 2. Check the EGR electronic controls.
be closed at idle) Refer to COMPUTERIZED ENGINE CONTROLS.





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



PCV valve malfunction Check the PCV system under TESTING
PROCEDURES.




AT OPERATING TEMPERATURE
Faulty canister purge 1. Check the Evaporative system under
and bowl vent valve TESTING PROCEDURES. If OK, step 2
2. Check the Evaporative System electronic controls.
Refer to COMPUTERIZED ENGINE CONTROLS.



Restricted exhaust system Check the Catalytic Converter under
TESTING Procedure"



Idle speed too low 1. Check and adjust idle speed under
ADJUSTMENT PROCEDURES.
2. Check the operation of all idle speed
control devices