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.
[1][2]C Charts



Air-Fuel mixture too lean
(restricted injector or plugged fuel filter) [1][2]Chart A-7 Fuel System Diagnosis


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



EGR at idle Testing and Inspection



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



Idle speed too low Check operation of any idle airChart C-2C Idle Air Control (IAC) System Check
control valve.