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. Exhaust Gas Recirculation
Flange gasket leaking,
valve open (valve should
be closed at idle)



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



PCV valve malfunction Check PCV system. Positive Crankcase Ventilation



AT OPERATING TEMPERATURE
Faulty canister purge Check Evaporative System. Evaporative Emissions System



Restricted exhaust system Check Catalytic Converter. Catalytic Converter




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