Midnight.Vibez

I just bought an 87 prelude that has a b20a swapped in it and the alternator belt belt snapped while driving it then the power steering belt was shredded. So I took the belt off then got a belt that would fit the alternator just so it will drive. After we put a belt in it we turned the car on to leave but as soon as I pulled I'm to the curb to wait for traffic the engine would idle up to 2000rpm then down to 1500 rpm. Its only at idle that it happens even while the car is rolling and I put in neutral it doesn't happen. I don't know what's wrong with it and why it's happening someone please help me I'm worried about it.

1funryd

Is this a 3rd gen Prelude or a 2nd gen prelude?
There were some 3rd gens that were built in 87, so we need clarification on what chassis you have because there are big differences between a 2nd gen and 3rd gen prelude.

2nd gen Prelude -




3rd gen Prelude -

Midnight.Vibez

After running the vin I found out it's a 91 thinking it's a 4th Gen could be a 3rd gen.

motoxxxman

that is a 3rd gen. the front bumper is from a 88-89 though.
There are a few different things that could be causing your problem. a vacuum leak is the most likely, or the FIV may just need to be taken apart and screwed all the way down (white plastic piece inside the FIV). FIV = fast idle valve, coolant temp controlled air valve on the back side of the intake manifold

boosted712

nice