High HC, Low or Normal CO - at Idle

Condition: High Hydrocarbons, normal or low Carbon Monoxide, at idle.

POSSIBLE CAUSE ACTION


Lean Air-Fuel mixture ^ Check fuel pressure.

^ Check O2 sensor.

^ Perform injector balance test.


Vacuum leak ^ Inspect vacuum hoses for proper routing and damaged lines.

^ SEE Vehicle Emission Control Information (VECI) label under hood.

^ Check intake manifold area.


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


Idle speed too low ^ Perform Minimum Airflow Test. NTC-17A Checking the Minimum Idle Air Flow