a couple of things to add, come to think of it. I think the distributor was rebuilt by "python". I knew it was some snake name or something.

He also said that if he sprayed carb cleaner or something like that into cylinder #4, it would smooth the idle right out. He said he was careful only to use a tiny bit.

He also mentioned that a backed up catalytic converter could be causing it, so that's one of the things he'll look at.