GM Service Manual Online
For 1990-2009 cars only

Results of Incorrect Operation

    • A plugged positive crankcase ventilation (PCV) orifice or hose may cause the following conditions
       - Rough idle
       - Stalling or slow idle speed
       - Oil leaks
       - Oil in air cleaner
       - Sludge in engine
    • A leaking PCV orifice or hose may cause the following conditions :
       - Rough idle
       - Stalling
       - High idle speed

Functional Check

With these systems, any blow-by in excess of the system capacity, from a badly worn engine, sustained heavy load, etc., is exhausted into the air cleaner and is drawn into the engine.

Proper operation of the crankcase ventilation system depends upon a sealed engine. If oil slugging or dilution is noted and the crankcase ventilation system is functioning properly, check the engine for a possible cause. Correct any problems.

If an engine is idling rough, inspect for a clogged PCV orifice, a dirty vent filter, air cleaner element, or plugged hose. Replace as required. Use the following procedure :

    • Remove the PCV hose from the cylinder head cover.
    • Operate the engine at idle.
    • Place your thumb over the end of the hose in order to check for a vacuum. If there is no vacuum at the hose, inspect for the following items :
       - Plugged hoses
       - The manifold port
    • Turn OFF the engine.
    • Inspect the PCV orifice in the cylinder head cover for debris or blockage.