A plugged valve or hose may cause:

A leaking or stuck open valve, leaking hose, or missing grommet may cause:

If an engine is idling rough, check for a clogged crankcase ventilation valve or plugged hose. Replace as required. Use the following procedure:

1. Remove valve retainer plug from the rocker arm cover.
2. Remove valve from the rocker arm cover.
3. Install the valve in the vacuum hose.
4. Run the engine at idle.
5. Place your thumb over the end of the valve to check for vacuum. If there is no vacuum at the valve, then check for a plugged hose at the manifold port, or valve. Replace plugged or deteriorated hose.
6. Turn the engine OFF and then remove the valve. Shake the valve and listen for a rattle inside the valve. If the valve does not rattle, then replace the valve

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

Proper operation of the crankcase ventilation system is dependent upon a sealed engine. Whenever oil slugging or dilution is noted, and the crankcase ventilation system is functioning properly, check the engine for possible cause and correct to ensure the system will function as intended.