1994 Saturn SC1

First thing I would do is check your little Z shaped hose that goes from your valve cover to you air box take it off let the car idle and see if the nipple the hose goes to on the valve cover is putting out a good amount of air. Thats your breather for the engine my guess is its plugged, or the hose, or the air box port it goes to is. Let me know what you find.

It's not too much oil pressure your talking about blow by building up and getting trapped in the engine that's differnt then oil pressure. What your talking about is the engine gases getting trapped and not releasing thru normal means like thru your valve cover breather. If the gases are not releasing and you have to remove the oil cap to release them then there has to something wrong with the valve cover breather or where it goes too. Because that connects to the same place your oil cap does. If it was working properly it would bleed down pressure thru the breather and you wouldn't have to remove your oil cap to release the pressure.