hello to everyone reading! i got my 91 running recently. the only issue i have left which i can’t pinpoint an issue is an engine surge on idle and anytime i’m not pressing the gas. it seems to rev on it’s own from rpms from 1k up to 2500. this only happens when the engine is warmed up enough. at initial startup, it idles at 2k. what could be my issue for this? so far, i’ve made sure there’s no vacuum leaks, so to my knowledge, it can’t be that. i have replaced my idle air control valve and cleaned it. any help would be appreciated and thank you in advance
Try this thread:
I think oxygen sensor and your FITV (fast idle thermal valve) might be your next checks.
If you go oxygen sensor, try to get the Denso. Some other brands just suck.
oops, forgot to add i also replaced my oxygen sensor, coincidentally it was a denso one, sorry. i will definitely try the fitv next and see if there’s any improvements. i’ll update with the outcome. thank you for the response
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update: fitv was definitely the issue, car’s been running great in idle for 5 minutes, car is still warming up but idle is at 1250 now. no surge, thank you for the help 
to anyone in need of assistance in the future, here’s what i did:
removed fitv, removed the 8mm/phillips one of the sides, used a flat to remove the wax and sprayed brake cleaner on all the parts, assembled it back together but please make sure to tighten that wax in very well but dont force it either. sorry if this isn’t so descriptive haha, phone’s in the process of dying.
update again: not fixed, any other leads as to why this could be an issue?
Have you tried spraying starter fluid around any vacuum lines, IACV or anywhere there can be a leak?
If you try that and the idle changes… it’ll be a vacuum leak where you sprayed. I’d try cleaning the IACV as well.
If the FITV seemed to fix it initially, try taking off the intake tube when it’s warmed up, put your thumb over the small hole in the throttle body (It’s where the air enters for the FITV) and see if it brings your idle back down… then it is the FITV and the cleaning you did just didn’t work.
I just posted this in another thread about the same issue. Are you driving an auto or manual? I was having this issue with my 91 automatic after my EGR valve (only on automatics) wasn’t holding a vacuum. It seems to happen whenever air isn’t flowing properly into the engine, be it vacuum leaks, gunked up throttle bodies, etc. If you’re driving an auto, this probably happens when you put it in park right? One thing to also check is your throttle cable. If it’s too tight such that the leaf is a bit open, that can also throw off the idle speed and so the computer will basically be “searching” for the right idle speed. I think some forum posts often refer to this issue also as “hunting idle” or “roaming idle.”
Here’s some other links and videos from my own research on the issue back when I was fixing it:
Surging/Hunting Idle when Parked
https://www.team-integra.net/threads/iacv-fitv-idle-problems-and-timing-adj.95330/
https://www.team-integra.net/threads/how-to-clean-your-fitv.105367/
https://www.team-integra.net/threads/how-to-clean-your-iacv.106451/