PCV Postive Crankcase Ventilation

What does the Positive Crankcase Ventilation PCV system do?

It removes blow-by gasses and crankcase vapors from the engine, diluting and replacing the contaminated air with fresh filtered air.

Air flows through the engine air filter, then to one side of the engine through a hose attached to the valve cover.  The opposite valve cover is connected to the PCV valve which limits PCV airflow into the intake manifold based on intake manifold vacuum.  The contaminated air is then burned in the engine and exhaust sent through the catalytic converter.  In the old days they just had a tube down low that pointed towards the rear of the vehicle to create vacuum that would exhaust the contaminated crankcase air into the atmosphere, burning is significantly cleaner.

All in all an extremely simple and efficient system.  As long as the engine nor the PCV system doesn't leak, doesn't get clogged and the valve operates properly you are good to go.  Sometimes the PCV valves stop working or it gets clogged, also all rubber hoses eventually fail which could lead to unfiltered air entering the crankcase or a loss of vacuum and a buildup of contaminated crankcase gasses.

Leaking valve or hose:

• Rough Idle

• High idle speed

• Stalling

• Excessive buildup of contaminants due to lack of scavenging

Plugged valve, hose, or filter:

• Rough idle

• Oil leaks

• Sludge in engine

• Oil in air cleaner

• Stalling or slow idle speed

• Excessive buildup of contaminants

At idle you can remove the PCV valve from the valve cover and place your thumb over the end of the of the hose to check for vacuum.  If you have no vacuum it could be the valve or a plugged hose or manifold port.  If you remove the valve and shake it it should rattle, if it doesn't it will require replacement though they sometimes can be cleaned.  Cleaning will not fix a broken spring or worn parts, obviously.