A positive crankcase ventilation (PCV) system is used on all Toyotas sold in the United States. Blow-by gases are routed from the crankcase to the carburetor, where they are combined with the fuel/air mixture and burned during combustion.
A valve (PCV) is used in the line to prevent the gases in the crankcase from being ignited in case of a backfire. The amount of blow-by gases entering the mixture is also regulated by the PCV Valve, which is spring-loaded and has a variable orifice.
On Toyotas, the valve is either mounted on the valve cover or in the line which runs from the intake manifold to the crankcase.
The valve should be replaced at the following intervals:
REMOVAL & INSTALLATION
Remove the PCV valve from the cylinder head cover or from the manifold-to-crankcase hose. Check the attaching hoses for cracks or clogs. Install a new PCV valve into the hoses, or reinstall in the cylinder head cover.
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. When blowing from the crankcase (valve cover) side, air should pass through freely.
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.