FREE REPAIR MANUALS & LABOR GUIDES 1982-2013 Vehicles
Courtesy of Operation CHARM: Car repair manuals for everyone.

High HC, Low or Normal CO - at Idle


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

POSSIBLE CAUSE ACTION


Electrical misfire ^ Inspect ignition system.
SEE IGNITION SYSTEM/ OSCILLOSCOPE PATTERNS.


Incorrect spark advance ^ Check spark controls.
SEE IGNITION SYSTEM/ TIMING SPECIFICATIONS


Lean Air-Fuel mixture ^ Check fuel pressure.

^ Check O2 sensor.

^ Perform injector balance test (SFI only).


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 COMPUTERS AND CONTROL SYSTEMS/ DIAGNOSIS AND TESTING.


EGR Valve open at idle ^ Check EGR system.