High HC, Low or Normal CO - at Idle

This condition, at idle, is indicated by abnormally high hydrocarbon emissions while carbon monoxide content remains normal or low.

POSSIBLE CAUSE ACTION


Electrical misfire Inspect ignition system



Too much spark advance Check and adjust timing, see
or initial timing advance ignition timing under "ADJUSTMENT PROCEDURES"



Air-Fuel mixture too lean Adjust air/fuel ratio, see "ADJUSTMENT PROCEDURES"



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



EGR at idle Check EGR system



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



Idle speed too low Check and adjust idle speed see
"ADJUSTMENT PROCEDURES"
Check operation of any idle speed
control devices