At Idle I have 17 in hg when I put truck in gear it drops to 15 in hg and idles rough, give her some gas and obviously I go into boost. completely let off gass while cruising and vacuum gos to 20 + in hg. I just dont know whats normal tor a turbo'd motor

 

vacuum gauge should be connected to an intake manifold source. 15 no load seems a little low. check for vacuum leaks. the rest is normal.

 

my cars does the same thing. Will sit at about 17 and when i shift into drive it goes down to about 15. only thign that i could come up with was to kick the idle up a LITTLE bit and then seemed to help my rough idle. Outside of that it is normal for a auto to drop a little bit of vaccum. ANyways what car are we wroking with here.