If you own a 2001-2002 Cougar with a 2.5L Duratec and are replacing your PCV valve, take note- the rubber boot at the bottom of the PCV valve is prone to ripping because it is very weak/thin rubber. A GOOD replacement for this comes with part:
YS4Z-6758-BA, which is a tube for the PCV system for the Focus.
The rubber boot on this is at least twice as thick and has the same size ports as necessary for the 01/02 2.5L
Also, the "PCV Valve" on the 01/02 doesn't really seem to be a PCV valve. There's no valve inside. It's just a little plastic tree, basically. Weird.
Anyway, tearing of this boot can cause a vacuum leak which may give you irregular stalling and/or performance.