To prevent the buildup of excessive pressure in the crankcase when the engine is operating is the job of the Toyota PCV Valve. This is the small cylinder shaped apparatus that is generally inserted into the valve cover on the Toyota engine and is connected to the intake system on your vehicle via a polymer tube.
The abbreviation PCV valve represents the word positive ventilation crankcase valve. This is a very descriptive name for the actual function of this component. The operations of the PCV valve is done to relive the pressure being constantly built up in the interior of the engine from the movement of the crankshaft and the blow by in the combustion of the fuel in the engine. If this simple little valve was not in place, the pressure would have to be vented in another place. In the past this venting of the pressure is why there were so many oil leaks on the engines of Toyotas of the past.
The Toyota PCV valve channels the gases from the crankcase and recycles it back into the intake system. This allows for the unspent fuel in its makeup to be reintroduced to the Toyotas combustion chambers so it can be more completely burnt.
The construction of the PCV valve is simple. It is a cylinder with a metal stopper that is held in place by a spring. When the pressure being exerted against it is more than the tension of the spring, the valve is opened permitted the flow of gases to exit the crankcase. The replacement of the PCV valve is necessary when the spring no longer has the appropriate tension in it or the valve itself become saturated with oil to the point it can no longer perform its duty.