High HC, Low or Normal CO - at Idle

This condition, at idle, indicates abnormally high Carbon Monoxide (CO) while the Hydrocarbons (HC) remain normal or low.

POSSIBLE CAUSE ACTION

Fuel Metering 1. Check Air/Fuel ratio, fuel pressure, and regulator operation.
2. Perform injector balance test.
3. Service fuel injectors (pressure cleaner).



Dirty air filters Clean or replace



Saturated fuel evaporative canister
or malfunctioning vapor purge system 1. See Evaporative Emissions System
If OK, go to step 2.
2. Check Evaporative System electronic controls.



Malfunctioning Closed Loop fuel metering
system - Exhaust leak or other false
indicators "Fooling" oxygen sensor to
sense a lean condition For testing of the computer feedback system, refer to Computers and Control Systems.



Stuck or restricted PCV
valve and/or hose See Positive Crankcase Ventilation