Anybody know anything about 90's vacuum controlled EGR systems? I've got one of those goofy little Japanese import trucks, and finding info about how it's supposed to work is a nightmare.

There's a pretty good vacuum leak out of the top of the vacuum amplifier/signal doodad. Kinda UFO shaped deal between the vacuum advance, intake manifold and the canister.

Any ideas on diagnosis, or ways I can figure out what's doing what would be helpful.