hi guys first post!!!
just got my prelude about a week ago and once and a while the idle would fluctuate, but most of the time it would just idle high (1500rpm). so today i decided to open the hood and see what was going on in there. the first thing that i noticed was that the fitv was bypassed. then i pulled my egr to clean it due to a egr code. and finally my iacv to clean as well. i put it all back together and started bleeding the air out of the coolant. as i was doing that it started fluctuating real bad. i took it out on the road and noticed that above 25 mph it would simply idle high, and then under the idle would fluctuate.... the drive-ability seams unaffected though

iacv?
tps?
vacuum leak?
the bypassed fitv?

 

oh and on cold starts or first starts of the day the engine will miss for a little then even out

 

i would think theres a vacc leak somewhere.

 

Welcome to honda-tech! Iin the future you should state which year and model car you have so we know what we are dealing with.

Bypassing/deleting the FITV stops the warm coolant from circulating the TB, it sorta acts like a choke on a lawn mower. You dont want warm intake air when its warmed up, but it does help on cold/first start ups. Un-bypass it if it bothers you, other wise slightly give it some gas for a minute or so when you start.

You know already what could be wrong, a vacuum leak, IACV, TPS, FITV.

If you cleaned the iacv, then make sure the tps is calibrated. I had a similar problem but turned out my clip was broke and it came loose on me. had to zip-tie it. Then check for leaks, nobody on here can tell you exactly whats wrong with the car.