I don't know if it's the same setup. But I had a 91 Mazda B2600 pickup that ran great for a long time. Then it started running funny, missing, etc. after 10-15 miles. Then soon after I couldn't get it to run decent for 5 min.

Turns out on this truck there were some parts in the computer that would leak and cause big problems. Here's a link to possible symptoms and what the company repairs. This is the company I used and they turned it right around and the truck ran like a champ after the repair.