PCV on 2001 Mercury Grand Marquis

PCV valves are on the rocker cover. You will either be able to pull it out or unscrew it. I am unfamilliar with the car so I am not sure which it will be. Try pulling it off and blowing carby cleaner down the valve, they can just become sticky, if it rattles when you shake it....Its probably working. A PCV valve is just a ball bearing sitting in a tube which vents crank case fumes and prevents backfires from entering. You should be able to blow through from the rocker cover side out, but not the other way. Make sure it is clean first though. :)

Scott.