High HC, Low or Normal CO - at Idle

CONDITION:
Excessive hydrocarbon emissions at idle speed. Carbon monoxide content normal or low.

HC's GREATER THAN 500 PPM

Ignition misfire: Inspect ignition system and repair as necessary.


HC's LESS THAN 500 PPM

Too much spark advance or initial timing: Check and adjust timing.

Air-Fuel mixture too lean: Adjust air/fuel ratio.

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

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

Idle speed too low: Check and adjust idle speed. Check operation of any idle speed control devices.