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 EGR system in "Testing
Flange gasket leaking, Procedures" in Emissions, if OK, step 2
valve open (valve should 2. Check EGR electronic controls in
be closed at idle) "Fuel Injection & Computerized Engine Controls"



Air management valves Check Air Injection system in
malfunctioning, no "Testing Procedures" in Emissions
air to ports while
in closed loop



PCV valve malfunction Check PCV system in "Testing
Procedures" in Emissions




AT OPERATING TEMPERATURE
Faulty canister purge 1. Check Evaporative system in
and bowl vent valve "Testing Procedures" in Emissions, if OK, step 2
2. Check Evaporative System electronic controls in
"Fuel Injection & Computerized Engine Controls"



Restricted exhaust system Check Catalytic Converter system in
"Testing Procedure" in Emissions



Idle speed too low 1. Check and adjust idle speed in
"Adjustment Procedures" in Emissions
2. Check operation of any idle speed
control devices