Rough, Unstable, or Incorrect Idle, Stalling

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, Check EGR system. See EXHAUST GAS RE-CIRCULATION
Flange gasket leaking, or SYSTEM in TESTING PROCEDURES.
valve open (valve should
be closed at idle)



Air management valves Check Air Injection system. See AIR INJECTION SYSTEM
malfunctioning, or no in TESTING PROCEDURES.
air to ports while
in closed loop



PCV valve malfunction Check PCV system. See CRANKCASE or POSITIVE
CRANKCASE VENTILATION SYSTEM in TESTING PROCEDURES.



COLD OR AT OPERATING TEMPERATURE
Faulty canister purge Check Evaporative system. See EVAPORATIVE CONTROL
SYSTEM in TESTING PROCEDURES.



Restricted exhaust system Check for a restricted exhaust system. See CATALYTIC
CONVERTER in TESTING PROCEDURES.



Idle speed too low Check idle speed or Idle Air Control (IAC). See
ADJUSTMENT PROCEDURES in TESTING PROCEDURES.