Originally Posted by bill buttermore
When you say that the engine wants to stall when you expose the crankase to the atmosphere by opening the oil cap, it makes me wonder if there isn't something wrong with the PCV valve or gaskets. It is cheap and easy to change and can affect the engine vacuum. .
I think I've heard this symptom before.
Is it possible there are two o-rings in the PCV now. Take it out and check again. I believe that'* what someone found when the car took in too much air when the filler was open to the atmosphere. Seal it off some and the bad PCV seal is mitigated.