I know the idle topics for B series have been beaten like a dead horse for years, I also have read countless forums on here about idling issues and what fixes what etc. Still no luck, I also keep finding myself trying to find very specific information that I cannot seem to find. So I decided to just make a post.

97 civic hatch, b16a2 (em1) swap, obd2a harness but ran on a obd1 p30 ecu (del sol b16 vtec ecu to be exact)
Other info: The car is a purposed built HPDE car, it only sees the street to go to the track, has no A/C, no radio, nothing. Its fully caged etc.

I have a idle surge problem, typical 1000 rpm to 1500 rpm. Start the car from a cold start, idles fine, a little high it seems after awhile but hard to say. Let the car run until it gets all the way up in temperature. The fan will kick on a few times and then it starts. The cars idle goes to **** and next thing I know it idles from 1000-1500 rpm constantly. I have also noticed if I start the car and just drive it immediately, it'll start surging instantly as soon as I put it back in neutral. Very annoying.

So, I have read plenty of forums and I know what the basic factors are in causing this idle problem. Examples like vacuum leaks, coolant not bled, IACV, FITV, Idle screw etc. First, I started with vacuum leaks, found none, all my hoses are new oem hoses as well so I can't see if being a cut hose or something. Also I feel if it were a vacuum leak, the idle would be bad no matter what. Unlike mine that is fine until I either drive it or let it warm up enough. Next up was coolant, bled the system completely no help, Third was my IACV, I read they can be cleaned. So I bought new hardware and an oem gasket and cleaned and replaced it. Installed it back in and nothing. I then decided why not unplug it and see if it helps or makes it worse. So I unplugged it and BAM! The idle stopped surging and it stuck at 1000 rpm (I know that idle is high, but im just trying to stop the surge first). So I turned the car off, turned it back on without the IACV plugged in and I get a 600 rpm idle, the car seems like its a little too low for its liking, maybe its me. Problem is I have a engine light obviously, so I plug it back in and the surge happens. I see some just unplug it and run it, but I am not sure on that. So my next idea was maybe my IACV is shot. So, since I am not a junkyard replacer, I go on Honda and buy a brand new one from Honda. I install it and bleed the coolant again since i lost some trying to remove the coolant hoses to the IACV. I turn the car on, bleed it etc, put the cap on and as I am doing this it comes back. The surging starts again.

So I am looking for opinions on what it could be, so far I know it cant be vacuum leaks, coolant, or my IACV. Could it be my FITV? I am concerned with doing that one since I am sure the screws are pretty shot to open it up. Could it be my idle screw? I know my idle is high but could that cause the surge? Is it my ecu?
Could I run the car without the iacv, obviously I know itll throw a code, but will it make the motor run rich? I know some say if you dont plug it in, and you have ac on, the idle will drop because the IACV isnt there to bump it back up so to say. But I dont have AC or heat or a radio etc. Nothing.

Also can you tune these things so they turn the IACV off? I have thought about running a Hondata, but it seems to be overkill for a idle surge. I am not really interested in power, just want my car to not sound like a rotary while im on grid waiting to go out on track!

All info is helpful! Thanks!

 

Check the map sensor!

https://honda-tech.com/forums/honda-...great-3006990/

 

Yes, definitely clean the FITV.. If the screws are/or get stripped use a reverse drill bit to back them out and then replace them with the correct diameter/pitch/length screws. Have you tried testing it per the description in reply #5 in this link?: https://hondaswap.com/threads/b16a-i...t-idle.101169/

You can try adjusting idle screw by counting the number turns in either direction while you are adjusting it and then returning it back to the starting position if adjustment doesn't help. As you stated it wouldn't correct a bouncing idle. If you try adjusting it use the procedure described in the service manual: https://honda-tech.com/forums/honda-...blems-2939616/

Finally, yes it could possibly be a faulty ECU. That should be the last item after all else is tested or cleaned. Can try swapping in a known good one if you know anyone with the same ECU

 

Okay I'll start with trying to clean the FITV, I tried looking for a reasonable condition oem b16a2 throttle body, but those seem hard to find. I have not tested anything related to the FITV. Mostly because I was under the assumption that the FITV was on warm up, then the IACV came in. Since my car does fine on warm up I thought it would be a waste. I'll take a look into my idle screw as well. I don't think its my ecu, could be, but I doubt it.

I will say I drove the car around to see if maybe it needed time to adjust or something. The surging isn't as consistent, still does it, but it'll try to correct itself. Then go back to surging then stop etc.

 

Have you tried checking the MAP sensor as wunfstgsr suggested in that link he posted?
Actually, cleaning the FITV may not help (but can't hurt) as it is used during cold start and not at operating temp.

 

I have not checked the MAP sensor, I've seen that post before and it seemed too specific and not really related to mine, he was missing a power wire in his harness for the sensor. I will check it though.

Yeah that's why I don't think its the FITV, I'll see how it looks and decide if I want to toy with it or not.