High HC, Low or Normal CO -- at Idle

Condition at idle: Abnormally high hydrocarbon emissions while carbon monoxide content remains normal or low.

POSSIBLE CAUSE ACTION


Electrical misfire Inspect ignition system
See Adjustments



Too much spark advance or initial timing Check and adjust timing.
See Adjustments



Air-Fuel mixture too lean Check for unmeasured air entering intake system. Also check for low fuel pressure and/or plugged or restricted injectors. See Fuel Delivery and Air Induction.



Vacuum leak Inspect vacuum hoses for
proper routing and damaged lines
Check intake manifold area



Leaking exhaust valves or piston rings Perform compression test and
cylinder leak down test



Idle speed too low Check and adjust idle speed
See Adjustments