if the vaccum is at 12... you have a leak somehweres. a 4G63 is suposed to run @ 18 in/hg... give or take 1. if youre only pulling 12 in/hg, you have a small leak somewheres.

and, the whole screw broke off and theres nothing there, not even the lock nut? i thikn wht you might have to do is send it back to GReddy and have them repair or replace it. its happend to a kid who tried to adjust the BOV w/ the nut, rather than the stud, and ended up stripping the threads. he said they replaced it for free. might wanna give them a call and see what they say. just tell them you were going to adjust it, and when you were undoing it, the stud twisted off w/ the lock nut.