i have a 90 civic with a ls engine swapped into it. problem is when it first starts it idles very high around 2k then as it warms it will "surge" at an idle lets say 8-12 minutes of run time from cold, at a stop light it will idle from 500-1500 rpm's. then after about 20 minutes of run time it will be fine and idle normally. any one have any clue what the cause of this may be? any help is appreciated or any links to answers on this subject

 

I've got the EXACT same problem with my b16a2 and can't for the life of me figure it out. It is driving me nuts! Any help/suggestions would be greatly appreciated!

 

vaccum or IAVC

 

Idle Air Control Valve.
Almost without a doubt-

 

thanks for the help is that a piece that can be cleaned or does it just flat out need to be replaced?

 

you can take it out and clean it but in some cases it needs to be replaced but rarely, just do a search im sure there is write up somewhere here

 

if it only happens while warming up then stops as the car is hot get the fitv
fast idle thermo valve which on a ls like a b16 i think its under the throttle body mounted to the intake manifold with 2 coolant lines going to it if i'm not mistaken one from the head to the fitv then from the fitv to the iac valve

 

Ok, take off your intake off the throttle body. You will see a hole about the side of your finger on the left hand corner of the throttle body opening. Take your finger in a sock,or shirt. Have your friend start up your car while you plug this hole. If your car idles normal then it is your FITV (fast idle thermal valve) You will have to take off this part which is located underneath the throttle body and unscrew the cap,tighten the wax-like part until fairly tight. Smooth idle is gained once again. If its not that,clean your IACV with carb cleaner,or check for a vacuum leak. 90% of the time its the FITV though.

 

exactly what boostedb20eh2 said fitv go out ALL the time, every friend i have with a honda has a plug off fitv
by the way how much power does your boosted b20 put down because i have a b20 and was considering boosting to put back in my car in place of my 18c motor

 

292hp and 218tq at 11 psi. Runs a 12.3. Check my sig for my full set up and feel free to PM me about anything