High HC, Low or Normal CO - at Idle

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

POSSIBLE CAUSE ACTION



ECCS system malfunction. Refer to On Board Diagnostics. Computers and Control Systems




Electrical misfire. Inspect ignition system. Ignition System





Initial timing incorrect. Check ignition timing. Ignition Timing



Air/fuel mixture too lean. Inspect mixture ratio feedback control. Initial Inspection and Diagnostic Overview





Vacuum leak. Inspect vacuum hoses for
proper routing or damaged lines and
check intake manifold area
for leaks.



EGR at idle. Check EGR system. Exhaust Gas Recirculation



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



Idle speed too low. Check and adjust idle speed. Idle Speed