Weirdest idle ever

[canx2k]

Hey guys,

New to the forum, so HI! I just purchased an 86' Prelude, and it has an odd quirk I'd like to iron out.

When starting from sitting after a few hours, my car's idle goes up to 1500, then down to 500, up to 1500, down to 500. And it's not gradual or anything. Once it warms up (ie driving 10 mins or so) the problem goes away. I'm annoyed with people staring at me at lights thinking i'm trying to race them.

How do I fix this problem?

[Si Speed]

I assume it's a DX carbed model?
Prelude85, where you at brother?

[Prelude85]

Yes, is it carbed or FI?

[runtingz]

ever since the swap my car does the same exact thing. but instead, after the engine is warmed up (5 minutes) during spring and summer, the idling craziness stops.
sometimes it looks like its going to touch zero but revs back up.

[THE ONE]

IACV needs cleaning and/or adjusting...

[canx2k]

Yes, I believe it is fuel injected. There's a light that comes on my dash that has pgm-fi, Does that help?

[Prelude85]

Yeah, that's Fi. . .how can you not know? =/

I don't know ish about FI, though. I've seen this problem arise a few times with the FI guys, unfortunately I didn't read up on it!! =/ Haha Ace probably gots it though.

I'm a carburetor cat. lol

[jonwz]

New Florida guy here with an '85 SI (FI). I get that idle behavior when there is an air leak in the spaghetti (all those rubber tubes). Sometimes you can hear the leak if you pop the hood and snoop around. It can be a hole in a tube, or even a loose tube.

[jerseytypesh]

Sounds like avacuum leak, make sure hoses are connected to where they belong

[the sr5]

i have the same problem!