been working hard on my b20 swap civic getting it ready for tune and i just cleared all the CEL codes - IAT, ECT, and TPS so now the only problem im really having is this idle, it doesnt happen on start ups but when im cruising and i go into nuetral is revs to 3-4k and ill have to tap the throttle for it to go back down and its not my throttle cable because when it stays at 3k rpms ill cut the car off and back on and its normal, i use to have a throttle cable problem where i would have to lift the pedal for the high idle to stop but i switched to a b series cable and bracket, got a less stickier oem b series throttle body and it was good for a bit but now my idle air control valve is my last resort. and i did bleed my coolant. i replaced my IACV with a cleaner oem but honestly if anything it made it worse. do you guys think its my IACV and where can i order a good one or can it be something else that im missing, ive adjusted my throttle cable several times and my idle screw but not the adustment screw for the throttle plate right by the body and cable. and its weird because i know my car will rev high when i go to nuetral so in 5th gear ill hit the throttle a bit before going into nuetral then itll rev down good. i do have a b18 intake manifold with a b18 IACV and all that.

 

Revving that high doesn't sound like a tune or IACV problem... I would be looking at the throttle body. Throttle wheel sticking, cable sticking (how about the crimped end of the rubber bellows on the throttle cable getting stuck on the throttle wheel), throttle blade sticking open slightly, FITV problems, weak return spring, improper throttle stop setting, etc. are all things that can cause what you are experiencing.

 

ok thanks jrcivic my question now is the FITV, is it suppose to be on the b20 with a b18 ls intake i think i have an extra throttle body with one if so ill add it. ill try adjusting the stopping screw its just weird how when it happens and i turn the car off and back on it idles alot better at like 1500 instead of 2500 - 4000 rpms and i dont suppose its my cable itself it seems perfectly fine ill check after work.

 

I wanted to join in the conversation, because my (stock) D16Y8 does this, but to a lesser degree. It only seems to happen in the morning (first start up), and will idle around 1700-2000 rpm. If, after the car is warmed up to operating temp, I’m still having the issue, if I blip the throttle in neutral, around 5-6k, it will settle down to normal (600-700) RPM. Mine also seems to be a non-mechanical issue, throttle return spring is nice and tight, nothing is catching / binding on the throttle body / linkage. Definitely seems like it’s either IACV, or somehow ECU related. Also, it’s pretty random, and does not always happen, and is also not always corrected with my “throttle blip”.