It is fitted in the rear valve cover, behind the throttle body. Screw off the PCV valve and pull it out of the valve cover; vacuum should be pulling on the valve when the engine is running. With the engine turned off, and slightly open the hood, make sure the engine is at normal operating temperature, place your finger over the end of the valve; if no vacuum is felt then examine for a plugged hose or valve and if any hoses appear plugged or deteriorated then replace them. When sourcing for a replacement PCV valve, consider the compatibility of the PCV valve with your car's make and the size of the engine before buying it, then closely compare the new one with the one that was replaced.