PCV valve should be checked every 20k miles or every 3-4 oil changes. You test it by removing it's hose from the port and blowing into it. You should feel a lot of resistance, and ideally not be able to blow into the engine. Then suck lightly and you should be able to draw in some oily smelling air from the engine. That is a proper working PCV.
We've noticed lots of problems with the PCV vacuum line on older Zetecs. The line will crack and leak vacuum, and sometimes the line will collapse under idle. Be sure to double check this line or replace it, or at least replace the rubber elbows. Ford makes an insulated replacement part that is better than the factory part for $20.
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Originally Posted by the user formerly known as ZX3_Chick
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