High HC, Low or Normal CO at Idle

This condition, at idle, indicates abnormally high Hydrocarbons while the Carbon Monoxide content remains normal or low.

POSSIBLE CAUSE ACTION

Electrical misfire Inspect ignition system.



Too much spark advance or initial timing Check and adjust timing. Refer to ADJUSTMENT PROCEDURES.



Vacuum leak Inspect vacuum hoses for damage and proper routings. Check Throttle Body to intake manifold area.




EGR at idle Check EGR system under TESTING PROCEDURES.




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




Idle speed too low Check and adjust idle speed. Refer to ADJUSTMENT PROCEDURES. Check operation of any idle speed controlling device.