So I have a 99 civic hatch with a 97 jdm gsr swap with a skunk2 IM, have an annoying idle surge that goes up an down between and 1-2, when I turn on AC it holds the idle at 15 every once in while, idk if i have a vacuum leak but I think I don’t due to that I replaced both the intake manifold gasket and TB gasket and bolted them down well. I replaced the IACV valve, MAP sensor and the TPS sooooo i really don’t know what’s up with my motor but I fr need help.

 

reset ecu, relearn idle.

 

The only way I resolved this on a H22 was to Block off the IACV completely.

 

Honda put in on like every motor for a reason. O.P is it a oem iacv ?

 

Does your car have an FITV? If the big "screw" inside the FITV backs all the way out, it will cause a surging idle.

 

It can't run without air. Find out how the extra air is getting in.

 

They also put in Catalytic converters, Evap Canisters, and a lot of stuff we delete every day.

 

On Del Sols hence Civics of the same era, the FITV would do that when warm. The fix is to unscrew the cover of the fast idle thermo valve (FITV), and screw back in the "big screw" or nut like DaX mentions. you have to finagle to screw it, but it takes 5mn and costs $0 to fix.

 

When my FITV backed out it only caused surge on cold starts, once warm it idled normal. And I agree with T-dog, reset ecu and follow steps to relearn idle.

 

Oh maybe you're right it was when cold? It's been a long time.
The alternate issue i think was with the EACV?

The FITV is purely mechanical if I recall - maybe with wax melting when the temp got high enough and that changes how it opens. A replacement to the manual starters of old cars.

nonetheless worth tightening just in case and go from there cuz it's easy to do.