GLHS 895

yo. i registered here to try and find out what's causing some problems on my friends car. since i can't post anywhere but here for the first two days i might as well drop it here. i don't know the guidelines of posting tech-questions, so let me know if it's out of place.
i'm also a bit curious about sentra's. i'd like to get my hands on one of those as a daily-driver. i wouldn't want to drive the GLHS daily. if something happened to that car i wouldn't be able to live with myself, as that car is irreplaceable.

anyway, my friend has no automotive fix-it knowledge. i've got a little bit so i decided to help. the only real experience i have is with mopars though, and that's mostly turbo 2.2's.

anyway, here's the rundown...

it's a 1980 280zx. it's got a straight-6 in it, 5-speed manual.

problem #1 seems to be a vacuum leak, but i cant find it for the life of me. it's making the idle really high, about 2000 rpms. i've also been told it "buzzes" every now and then but when i was with the car i didn't hear it. turning the screw on the throttle body fixes it temporarily, but the leak is intermittent, so when the leak goes away the engine dies. is this just a vac leak or something else?

#2: the car diesels a little bit when you shut it off. don't know what it could be.

thanks for any help. later.