I spoke to a friend who completed the test successfully on a Mitsu 3000 GT, VR4. It is important to disconnect and plug the PCV. That will cause the crank case to pressurize, including the oil pan. That in turn could lift oil seals off of their seat and cause oil leaks.
I don't want to sound like too much of an alram, but, I would reccomend you don't try this test anymore UNLESS you disconnect the PCV and plug it first. I am sorry I didn't think of it before.
Also, the friend indicated that the place through which the air pressure "vanishes", is the oil fill cap.
He had some comments about the injectors possibly lifting off of their seals, even after taking care of the PCV route, but neither him nor me were convinced that this was going to be a serious problem.