Toyota Corolla 1970-1987 Repair Guide

Positive Crankcase Ventilation


See Figure 1

A closed, positive crankcase ventilation system is used on all models. This system cycles incompletely burned fuel which works its way past the piston rings back into the intake manifold for reburning with the fuel/air mixture. The oil filler cap is sealed and the air is drawn from the top of the crankcase into the intake manifold through a valve with a variable orifice.

This valve (commonly known as the PCV valve) regulates the flow of air into the manifold according to the amount of manifold vacuum.

A plugged valve or hose may cause a rough idle, stalling or low idle speed, oil leaks in the engine and/or sludging and oil deposits within the engine and air cleaner.

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Fig. Fig. 1: PCV valve system on a carbureted engine-most engines similar


Remove the PCV valve from the valve cover or camshaft cover. Remove the hose from the valve. Take note of which end of the valve was in the manifold. While the valve is removed, the hoses should be checked for splits, kinks and blockages. Check the vacuum port (that the hoses connect to) for any clogging.


A leaking valve or hose could cause an erratic idle or stalling

Check the PCV system hoses and connections, to ensure that there are no leaks; then replace or tighten, as necessary.

To check the valve, remove it and blow through both of its ends. When blowing from the side which goes toward the intake manifold, very little air should pass through it. When blowing from the crankcase (valve cover) side, air should pass through freely. An alternative method may be to remove the PCV valve from the cover and shake it end to end, listening for the rattle of the needle inside the valve. If no rattle is heard, the needle is jammed. Replace the valve with a new one, if the valve fails to function as outlined.

Do not attempt to clean or adjust the valve; replace it with a new one