Hello. I just came on here looking for help because of the same problem, and mine was a cap that popped off. I drove home in my Explorer last night, and it ran fine, but this morning it stalled repeatedly at startup, and even though I got it to idle a little better, I could clearly tell something was wrong, in addition to the bad idle, I heard the vacuum leak. I popped the hood, and saw the cap sitting on my exhaust manifold, but couldn't figure out where it came from. After seeing the pics posted by arpac90, I went out and looked, to see the spot on the manifold where it went. I have now checked out everything else, and the PCV is as it should be.
After reading everyone's post, it sounds like there is more than one configuration to the vacuum lines on these engines. I just figured that I'd post up my info to possibly shed additional light on the subject.