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.



Incorrect initial timing Check and adjust timing, under ADJUSTMENT PROCEDURES.



Vacuum leak Inspect vacuum hoses for damage and proper routings. Check the 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, under ADJUSTMENT PROCEDURES. Check operation of any idle speed controlling device.