Major Trooper Idle Problem, Help please!!

Hi, i own a 1992 isuzu trooper, and was wondering if anyone can help me with my problem. 3 weeks ago it took a long time for it to start, but other than that it ran fine. 5 days later i was driving it, and it stalled in an intersection, and took a few tries to start it again. next day, same thing. so i took it to the garage, and now, 2 weeks later, they still dont know the problem. And now it just sounds awful, its sputtering and running real rich, and bogging itself down. it sounds like a 70 year old truck now. it'll run for a minute or a few seconds, then stall. The spark pluggs were changed, a tune up was done, but still no success. they dont want to throw any parts at it, until they know the problem, and they cant find out the problem because they cant scan the computer on it. they cant seem to get an adapter for it so they can plug into the outlet. and i dont think anyone else near me can either. Any ideas? please help,
Bryan.