This is a really weird solution, but believe me it worked for me! My 1999 VX starting doing this periodically and I could not find a solution. Check EGR valve as noted on this site. Nothing! Check fuses. Nothing.

Took it to the Isuzu place here in town and it would not do it while they had it there (always makes you look like a fool!!).

Finally it did it on the way to work one day, so I drove straight to the shop. As soon as the meter went on, it slowed the idle down! Tech looks at me and says everything was running fine, but he was very interested now. After a long look, he noticed that the left wiring harness to the computer, under the CD player, when wiggled stopped the reving. Told me to keep track of it... if it did it again. Took two months to do it again, but when it did, I took off the cover and carefully wiggled the harness and it went away. That night I crawled under the dash and noticed that the movement that was fixing it was to push back on the wires in the harness(toward the firewall). I very carefully pushed back on the harness and tighten the clips to hold it back alittle...has not done it again in several months!!! Was so scared the it was the connection to the computer board and was going to have to buy that.

I think it was just riding up on the cover plate till it quit making contact on the underside of the connector/clip.

I know it sounds weird...but it's been working for sometime now. Give it a try.