A positive crankcase ventilation valve. It uses vacuum from the intake manifold to draw fumes from the crankcase. Symptoms of a faulty PCV valve are poor idle and excessive pressure in the crankcase.
An emissions control device that allows gases from the crankcase to be reintroduced into the intake.
A valve usually located in the rocker cover that vents crankcase vapors back into the engine to be reburned.