My 99 D starting having this same problem all of a sudden a few days ago. I took it to the dealer and they replaced the idle control valve, and suggested I get a new battery, and clean the throttle body...but I declined those. It drove great on the way home, but did the same thing 2 days later. I'm glad to see this post. I'll try the resetting of the PCM tonight. And if it doesn't remedy the problem for long, I'll try getting the PCM rebuilt as t-bank did. Thanks a bunch!