Scotty I’ve been working on my friends 1990 Suzuki Sidekick 4WD 5-speed with 250,000 miles on it. It sat for 3 years in my friends yard without running even once, when we started it up again it was running like crap. We discovered that it had THE ORIGINAL spark plugs in it with 250,000 miles on it! So we changed that along with the distributor, brakes, tires, and some exhaust work that needed to be done on it.  It’s running good now except for one thing that we can’t figure out and neither can our local Mechanic who specifically works on Suzuki’s. It revs up and down while idling up to 4000rpm even at first start up but doesn’t do it while driving. What could be the problem?