GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Positive Crankcase Ventilation (PCV) Valve


See Figures 1, 2 and 3

The PCV system must be operating properly in order to allow removal of fuel vapors and water from the crankcase. This system should be checked and serviced every year or 15,000 miles. The PCV valve should be replaced every two years or 30,000 miles. Normal service includes cleaning the passages of the systems hoses with solvent, inspecting them for cracks and breaks, and replacing them as necessary.

The PCV system is designed to prevent the emission of gases from the crankcase into the atmosphere. It does this by connecting a crankcase outlet (usually the valve cover) to the intake manifold with a hose. The crankcase gases travel through the hose to the intake manifold where they are returned to the combustion chambers to be burned. If maintained properly, this system reduces condensation in the crankcase and the resultant formation of harmful acids and oil dilution. A clogged PCV valve will often cause a slow or rough idle due to a richer fuel mixture. A car equipped with a PCV system has air going through a hose to the intake manifold from an outlet on the valve cover. To compensate for this extra air going to the manifold, carburetor specifications require a richer mixture at the carburetor. If the PCV valve or hose is clogged, this air doesn't go to the intake manifold which makes the mixture too rich and results in a slow, rough idle. The valve should be checked before making any carburetor adjustments. Disconnect the valve from the engine or clamp the hose shut. If the engine speed decreases less than 50 rpm, the valve is clogged and should be replaced. If the engine speed decreased much more than 50 rpm, then the valve is good. The PCV valve is an inexpensive item and it is suggested that it be replaced. If the new valve doesn't noticeably improve engine idle, the problem may be a restriction in the PCV hose. For further details on PCV operation refer to Driveability & Emissions Controls of this information guide.

Click image to see an enlarged view

Fig. Fig. 1: Gasoline engine PCV system flow.


  1. Grasp the valve and withdraw it from the valve cover.
  3. Holding the valve in one hand and the hose in the other, carefully pull the valve from the hose and remove it from the vehicle.

Some PCV valve hoses will be retained to the valve using a clamp. If so, use a pair of pliers to slide the clamp back on the hose until it is clear of the bulged area on the end of the PCV valve nipple. With the clamp in this position, the hose should be free to slip from the valve.

  1. Check the PCV valve for deposits or clogging. The valve should rattle when shaken. If the valve does not rattle, clean the valve with solvent until the plunger is free or replace the valve.
  3. Install the PCV valve to the grommet in the valve cover.
  5. Connect the PCV hose to the valve.

Click image to see an enlarged view

Fig. Fig. 2: On some models, it may be necessary to remove a clamp on the PCV hose

Click image to see an enlarged view

Fig. Fig. 3: Once the clip has been slid back on the hose, the valve can be removed