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 the On-Board Diagnostic System for fault codes. Refer to Computers and Control Systems, Reading Diagnostic Trouble Codes


Air-Fuel mixture too lean Check the On-Board Diagnostic System for fault codes. Refer to Computers and Control Systems, Reading Diagnostic Trouble Codes


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


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



Idle speed too low Check the On-Board Diagnostic System for fault codes. Refer to Computers and Control Systems, Reading Diagnostic Trouble Codes