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 initial timing ^ Check Distributor Assembly installation.


Incorrect spark advance ^ Check spark controls.


Lean Air-Fuel mixture ^ Check Air-Fuel ratio, O2 sensor, perform injector balance test, inspect regulator operation (check vacuum line and return hose), check fuel pressure.


Vacuum leak ^ Inspect vacuum hoses for proper routing and damaged lines Check intake manifold and components.


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


Idle speed too low ^ Check operation of Idle Air Control (IAC) motor.


EGR Valve open at idle ^ Check EGR system. Exhaust Gas Recirculation


Restricted PCV valve and/or hose ^ Check PCV system.