Hey, folks. Haven't posted anything in a while, used to be a somewhat regular poster. Usually if I know the answer to a question, somebody else answers it before me anyway, so I've been sitting back and looking.

I have a little issue with my truck. It's a 1998, 5.9, auto, 165k. It has a surge / flat spot in acceleration. It is most noticeable in 3rd gear, and honestly I've only noticed it when running the AC. When you're accelerating slowly, or keeping steady throttle, somewhere around 2k rpm's, it will sort of act for an instant like you eased back on the throttle a bit, then got back on the throttle again. You can watch the tach go south for an instant when it does it. It doesn't lose all power or anything, just feels like you're mashing and letting off the throttle a bit.

The truck idles smooth, and I did the plenum fix 15k miles ago or so. My first thought was TPS, but I got a new one from the dealer and it did not fix it. It's not a huge surge, but you can feel it and hear it with the magnaflow muffler I put on some time back. Anyone have any ideas? Ever heard of the AC compressor / bad connection there causing this?

 

Check your serpentine belt, tensioner, and idler pulley, sounds to me like the belts slipping. The extra load from the compressor could explain this.

to check belt: Examine for small cracks

to check tensioner: try to move it by hand, if it does without considerable force its toast

to check idler pulley: watch with engine running for wobbles or squeaks.

 

I did just put a new tensioner on there, actually one off an 01 that came in the scrap yard. Should be good. It did it with the old one too, old one you really had to push hard to release tension and it would spring back really slow. New one can push it in, but you've gotta use a fair amount of force, and it returns when you let it go.

Idler pulley seemed alright when I spun it by hand.

Wonder if the belt could be stretched? It's been on there a while, is a Gatorback belt and I've left it on there because it rarely ever squeaks (which most others I tried seem to squeak).

I'm also wondering about the alternator, it's original. Maybe it is nearing the end of it's life, sending a bad signal when AC is on to pcm, tps, or some other sensor abbreviation.

 

http://motorheadsdiygarage.com/wp-co...TINE-BELT1.jpg

If your serpentine belt looks anything like that one, id start with replacing it and see if that helps.

 

i had a similar problem take your throtlle body apart and clean it, also clean the hell outta the iac and where it plugs into, maybe look into doing plugs, wires, cap and rotor as well.