See Figures 1, 2, 3, 4, 5 and 6
The PCV valve, which is the heart of the positive crankcase ventilation system, should be free of dirt and residue and in working order. As long as the valve is kept clean and is not showing signs of becoming damaged or gummed up, it should work properly. When the valve cannot be cleaned sufficiently or becomes sticky and will not operate freely, it should be replaced.
The PCV valve is used to control the rate at which crankcase vapors are returned to the intake manifold. The action of the valve plunger is controlled by intake manifold vacuum and the spring. During deceleration and idle, when manifold vacuum is high, it overcomes the tension of the valve spring and the plunger bottoms in the manifold end of the valve housing. Because of the valve construction, it reduces, but dies not stop, the passage of vapors to the intake manifold. When the engine is lightly accelerated or operated at constant speed, spring tension matches intake manifold vacuum pull and the plunger takes a mid-position in the valve body, allowing more vapors to flow into the manifold.