Oil cap or PCV valve...

I brought a Montana ´97 back to Sweden that I'm trying to keep rolling (not too easy given the spare part prices here..). Anyway my 3.4L engine has recently started to "die" when it gets up to working temperature. This phenomena stops when I loosen the oil fill cap. Is this because the PCV isn't working or what?
Besides, I love this roomy van that makes Volvos look like "beetles"

Checking the PCV valve is simple enough. Lift it out, and stick a small screwdriver up the end of the PCV valve that goes into the engine. The little door should open and spring back freely. If it's sticking, you can either soak the hole unit in gas to try and clean all the gunk off it, or replace it (they're inexpensive).

Hope this helps....

I checked the PCV valve and it seems to work fine. Think it was replaced at the same time the manifold gasket was fixed...
I guess the valve leads vapours out... is it related to idle rpm? My problem only occurs when the engine is idling

I would suggest checking CAREFULLY all the vacuum lines for possible leak firs.

Greets
Zebe