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,
Flange gasket leaking,
valve open (valve should
be closed at idle) 1. Check EGR system
If OK, proceed to step 2
2. Check EGR electronic controls.



PCV malfunction Check PCV system



At operating temperatures

Faulty canister purge 1. Check EVAP System.
If OK, go to step 2.
2. Check Evaporative System electronic controls.



Restricted exhaust Check Catalytic Converter



Idle speed too low Check operation of any idle speed controlling device. Check and adjust idle speed