Won't start

The engine idles a bit rough, so I may have a vacuum leak somewhere, but I haven't started trying to isolate it. Oh... While I'm on the topic of potential vacuum leaks, I have a problem with the back top bolt on my intake/exhaust manifold coming loose, and I constantly have to retighten it. It's currently got a white residue around the one bolt hole (coolant?), and I had to replace the gasket a few months ago because it had burned out back there. Seems to diesel when I let that bolt loosen too much.
Is it a bolt? It should be a stud and nut with a special triangular washer. If it is a bolt, and you're constantly torquing it, it is likely wearing the threads out in the head.

See here: Manifold Mounting