I can't believe what the problem turned out 2 B! Was the plenum gasket (gasket between upper and lower intake manifolds); there wasn't much left of it ; can't believe the truck even ran at all. I guess U can thank the Ford computer. My F-150 4X4 ( the one I just took the upper intake off ) had a terrible idle problem. The truck is an '89 ( with 302 & 5-speed) and I've had it since '92. The truck would never idle below about 1,100 RPM when I first purchased it. Over the years it became progressively worse. It got 2 the point that it would not run below 1,700 just this past weekend. I couldn't stand it any more...as this would wear out my original clutch! This truck has 136,000 miles on it now; had 46,000 when I bought it back in '92. I just finished cleaning and getting everything perfect and reassembled with new gasket & sealer better than the factory. The truck runs better now than it ever has since I owned it!!! I can actually adjust the idle where I want-800-850 RPM! Wow what a difference! I just can't believe it! And 2 think, I posted the "high revving idle" question on every board know 2 man and no-one guessed it!.hehehe I'm tickled! Am I tooting my own horn?....forgive me board. Thanks guys 4 all your replies.