This is for high and roaming idles but may work for low idles as well.
First, terms:
TB – Throttle Body
IM - Intake Manifold
IACV – Idle Air Control Valve (also called the Electronic Air Control Valve or EACV)
FITV – Fast Idle Thermo Valve
TPS – Throttle Position Sensor
I finally got the swap (b18a) in my civic. Unfortunately when I started it up it idled at 3k and then had a hunting idle from 2k to 2500 rpm when it warmed up. I stood over that thing for 3 days, testing and scratching my head. On top of that I did a TON of searching on the h-t, hybrid boards, and on here. I hope what is contained within helps someone. Maybe they wont have to go through as much work as I did.
The idle on our Hondas is a tricky thing. It is controlled by two main sensors: the FITV and the IACV. The FITV is a mechanical valve that is controlled by coolant temperature (there is no ECU plug to it). When the coolant is cold the valve is open and letting air into the IM through a hole in the TB before the throttle plate. This essentially creates a small vacuum leak which in turn lets the motor idle higher than normal (supposed to be around 1500-2k for warming up). As the coolant warms up the valve closes and no longer lets air in through the hole in the throttle body. All the while the IACV, which is ECU controlled, is letting small amounts of air into the IM through another hole in the TB. Any amount of extra air the ECU is not expecting will confuse it and you will get either a high idle or a roaming/hunting/fluctuating idle. On to the troubleshooting.
First things first, don’t skip any of these steps. From what I have read (and experienced) usually small dumb things cause these problems so don’t overlook anything. Also refer back up to the pictures if need be.
Check your vacuum routing. On the underside of your hood there should be a vacuum diagram. If there isn’t a diagram under there, there is one in a Helms, Chiltons, or Haynes manual for your car (you should have one of these anyway). Remember, ANY extra air will confuse the ECU. Check for cracked or bad vacuum hoses. If in doubt just replace the hose, they are cheap.
The PCV valve could also be the culprit. Take it out and examine it. If it is cracked it could be causing a vacuum leak. Replace the peice if you arent completely sure it is ok (the helms/chiltons/haynes manuals tell you how to check it).
Check to see that your throttle plate is closed all the way. Take your intake off at the TB and check to see that nothing is blocking the plate. If nothing is in the way and it isn’t closed all the way, loosen your throttle cable.
Check to see if the nuts holding the TB and the IM on are tight, this was the source of my idle problem. If they are loose, tighten them.
Bleed your coolant. Some air bubbles may throw the FITV off and keep the valve open.
Take the 3 10mm bolts out of the FITV (you don’t have to take off the coolant lines). Then take off the 2 8mm bolts off the plate on the back of the FITV. Once the plate is off you will see a white plastic thing, screw that all the way in. This causes a TON of people’s hunting idle problems (it’s a source of a vacuum leak). Put the FITV back on and start the car up. If it still idles bad go on.
Clean the IACV screen(s). See Oz’s write up elsewhere on G2IC.
Make sure your car is completely warmed up. With it running, take the intake off the TB. There are 2 holes right in front of the throttle plate, these are the holes that feed the IACV (top hole) and the FITV (bottom hole). With your finger, cover up the bottom hole (it should NOT be sucking if your car is warmed up). If the idle goes down the FITV is to blame, either get a new one or take it apart and screw the valve completely closed (I have only read of people doing this, so I don’t know exactly how. Also, you will have to keep the engine speed up yourself when the car is cold).
Next cover both holes up with your fingers. The car should sputter and die (or almost die). If it does then the source of your crappy idle is the IACV. Replace it. If you want you can test the IACV. Shut the car off and put + battery voltage to the blk/yel terminal (on the valve) and momentarily touch ground to the blu/yel side. When doing this the valve should click, if it doesn’t, replace it.
If, when covering both holes the car still has a high idle, you have a vacuum leak somewhere. Again check the IM and TB nuts. You can spray carb cleaner around those areas and if any gets sucked in (the engine will rev) you have found your leak. Another source of vacuum leaks are where the FITV and IACV connect to the IM. Either replace the gaskets or use silicone gasket sealant.
If nothing has worked you should test your TPS. Probe the middle wire on the TPS plug (with the key on but not running, and the plug still connected to the sensor) with the + probe on the volt meter, and the neg probe to ground. You should have .5v with a fully closed throttle plate and 4.8v with it wide open. If the TPS is off, replace it. My TPS was .425v to 4.55v and it idles fine now so I don’t know how big the margin of error is. Also, it is pretty rare for these to go bad.
If, still, nothing has worked you might want to try a new ECU. This also is very unlikely, but worth a try.
If it still idles bad, go through the steps again.
I really really hope this helps someone out. It was a pain to have this mysterious problem and very little info on how to go about troubleshooting it. Comments or suggestions are welcome.
I had almost the same exact problem as you had with your Civic. A friend and I installed a B18B into my 90 LS, and when we first started it up, the idle went straight to 2500 and then dropped to 1000, and after warmup, it would fluctuate from 1000-1700. I can’t stress how important it is to check the bolts around the IM and TB. I spent 2 weeks trying to find the problem of my idle fluctuation. Finally, we brought the car to a friend who’s one of the lead mechanics at an Acura dealership, and he told us to swap out the 90 IM for a 94+ IM. He said the 90 IM was not letting in enough air to the engine, and the ECU was trying to compensate for the loss of air. I thought that was weird, and since I ran out of solutions, I thought it was worth a try. I went to a junkyard to purchase a 94 IM and proceeded to bolt it on. When I started to disassemble the 90 IM from the head, I noticed at least 3-4 bolts were relatively loose. I really think this was the problem all along, but I decided to go ahead and replace the 90 IM with a 94 IM anyhow. The 94 IM bolted up just fine, and I didnt have to use the Fast Idle Control Valve anymore, due to the lack of a mounting option on the 94 IM. After going through all that trouble, I’m pretty sure I could have saved myself some money and just tightened the bolts around the 90 IM instead of replacing the IM with a 94 IM. The write-up you just did on the idle problem should be archived. Again, great write-up, and glad to hear you fixed your idle problem as well. You can check out my posts on this problem to see all the trouble I went through.
Yeah, I read through your thread, it gave me lots of ideas on how to maybe fix mine. Keep the 94 IM, the B18B IM’s flow better. How much did yours cost?
The idle problem was a real PITA because there are so many things that cause the same result (the hunting idle). I have read through soooo many posts over at honda tech describing the exact same problem I had but when I PMed them, they all had different fixes. I hope this covers all of the possibilities. If I skipped over anything PLEASE let me know.
I still have to take pictures. But rest assured, there will be lots of pictures.
I paid 50 bucks for mine from a local junkyard over here in the bay area. The dealer wanted $350! It does seem to have a larger plenum than the 90IM. I agree, the idle problem I had was a PITA! So many things could have been the problem, and the fact that I didnt get a check engine light so I can check any error codes, didnt help at all. I think you covered all the bases on this problem. This is definitely the best write-up so far. When I had my problem, I searched and searched all over the web, and couldnt find anything to really pinpoint my problem. Looking forward to seeing those pictures.
Pictures added. I thought it was going to take more pics but it didnt. I dont have a pic of the white thing because I’m not going to take off the FITV again.
Originally posted by Ben Ogle
[B]Pictures added. I thought it was going to take more pics but it didnt. I dont have a pic of the white thing because I’m not going to take off the FITV again.
i decided to check my stuff and again and noticed im still getting suction from the fiv while warm. so i took it apart and did the writeup, but alas, still suction.
hopefully thatll be the cause of my slight (barely noticeable) bounce at idle and i wont have to take apart the iacv again so i can get a higher idle while in gear/ac on…
ARCHIVETHIS saved me $80 if I had saw this a year ago would have saved even more and saved time and frustration. Have already swapped 2 FITV (used) for same problem in past
Thanks for the info.
Thanks to this post, my car now idles perfect again. My FITV was the culprit. I took it apart and tightened that white screw thing and it’s fine now. Thanks for the help. This is a very good troubleshooting article!
I looked at how to take the FITV off my TB yesterday and there was something in the way of the top bolt holding the FITV there. My question is, do you have to take that thing off?
(I don’t know what it is, but it’s shown in your pictures)
A normal socket wrench won’t fit in there to take off that bolt.
Thanks.
You dont have to take the FITV off. You can screw the plastic thing in just by taking one bolt off the end plate and swinging it out of your way. I dont know whats in the way if the mounting bolt, though. Mine came off fine.
wow, im so glad i found this thread, my teg’s been iddling pretty bad lately. im go along with this. THANX A LOT BEN OGLE!!
also …when are you coming out with another batch of your famous OgleSport Rear Lower Tie bars? If you could please let me know, i’ll be waiting patiently…
Ok heres a new one for yah guys , this is caused by racing so im sure one you have encountered it or have it now , i call it the jumping idle syndrom , which is the idle jumps from 800 to 1500 and back and forth 800 1500 back and forth , well this is caused by that thing you guys are talking about but this can cut down performence as well , which means less air for your fire breathing B engine,less air means less combustion , means less horse power , so listen up , this is gona boggle your mind , eliminate it all together as in lets solve the problem from the source , lets get ridd of it alll together no more valve, try sticking your finger in the bottom hole in the throttle body , idle should go to normal , (sometimes its the one on top depending on the one you have blown,) about 900, so what are you going to do chop your finger off ,and leave it in there or you can get a 5/16 rubber nipple from your favorite place auto zone and stick it in there , it should be tight enough to stay in the hole by it self and the vacumm causes a seal so tight no air escapes which means youve bypassed the whole valve and also you have given your computer a break , so you get better gas miledge, you will also notice a boost in power, and plus it cost 1.50 for the part , word of caution you may backfire if you stall out, and it will spit the nipple out, and you may get it sucked into the manifold , but not to worry youll get a surge in rpms , and a puff of black smoke from the exploded nipple but not to worry you got 3 more in the pack from auto zone , so just pop it right back in there
-i checked for vacum leaks on the lines …didnt find any
-checked to see if throtle plate is closin all the way . It is. (on a side note: there a lot of black stuff on the throttle plate, almost as if it got burned. Where could this have come from).
-took FITV, and its back side. The white plastic thing WAS really loose. So i tighented all the way in.
Just cuase i was alredy workin under there, i took the IACV off and i cleaned it (using oz’s write up)
-i put everythin back together…
now car idles between normal and really low. even has shut off couple times.
any ideas?
i really need to get her working
pleassse.
P.S- car was idling funny before, but never this low, and wouldnt shut off
The black stuff is normal, I promise. Every motor or TB I have seen has had black stuff (I’m thinkin oil residue) on the throttle plate. Try resetting your ecu. If you want you could adjust the idle screw on the top of the TB. I dont know what else you could do. My obd0 b20 idled low too. But I just made a chip that bumps the idle up like 40 rpm and it is working fine.
R@ce, I dont know wtf you are talking about. The first post I made has all that same info. if you are sucking air into the bottom hole then you need to fix your FITV. Its not caused by racing.
Originally posted by Ben Ogle
[B]The black stuff is normal, I promise. Every motor or TB I have seen has had black stuff (I’m thinkin oil residue) on the throttle plate. Try resetting your ecu. If you want you could adjust the idle screw on the top of the TB. I dont know what else you could do. My obd0 b20 idled low too. But I just made a chip that bumps the idle up like 40 rpm and it is working fine.
R@ce, I dont know wtf you are talking about. The first post I made has all that same info. if you are sucking air into the bottom hole then you need to fix your FITV. Its not caused by racing.
Ben [/B]
well mr smart guy , you must not know alot so ill lower my iq to yours so i can expalin, you know that thingy that the air goes into and it goes into that thing and mixes with that gassy stuff and blows up , well this is a normal process , add more power stuff and something they call horse power your bound to blow something ,as the weld s (gum looking things ) are made to fold when under pressure as not to blow black smoke out with a gang (backfire) so since those japs guys are smarter then YOU they made it so you wont detinate , oh sorry blow up you motor , soo, maybe since your car maybe slow , and you dont experience lots of vrooom vroom then maybe you should take you moms car and sell it for a ford ,
