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 (MPI).



Vacuum leak Inspect vacuum hoses for proper routing and damaged lines.
Refer to 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.
SEE Powertrain Management/Computers and Control Systems/Testing and Inspection/Procedures.