1994 Mitsubishi Expo (160k mi) starts fine after a rainy night, runs well for a few minutes, then runs (sometimes very) rough, especially under load. Car is fine if it runs for another few minutes, but if shut off during the rough stage is very hard to restart. I have sealed the wires and cap, no noticeable wetness under the hood. Any ideas?
What do you mean you’ve “sealed” the cap and wires?
I’d say its time to replace 'em.
My guess is the poster sprayed the wires, etc. with an ignition (silicone) spray.
I’ve done this myself, but only AFTER installing new wires and plugs, etc.