First off, car is a 93 civic SI with a OBD1 B16A.


Ok, gonna give every detail so you guys dont just think im a idiot who hasnt looked into it before this post and such.


Started out car would idle ridiculous high when cold, and then idle normal 800 when warm. I checked the FITV and it was all the way loose, screwed it in and it was perfect. Idled perfect all around.

Few weeks later, starts idling fine when cold, but when warmed up it would idle at <500, almost setting on the needle stop on the cluster like, really damn low.

So I thought somehow me screwing the FITV all the way in would maybe have a effect on it. So i removed the FITV and ran the coolant line from the IM straight to the IACV, and used a alumnium plate with a gasket maker sheet between it to bolt up where the fitv was. Started the car up, idled normal cold, but still low when warmed up.


So i remove the IACV, and see a clogged screen. I say, sure thats got to be it. So i clean the **** out of it, dry it out thoroughly, hook it back up. Idles fine cold, but still really low when warm.


Keep in mind, i changed the TB gasket while i was at it, I pulled the idle screw and cleaned all gunk out from all passages on the TB and everything, so its nothing that needs to be cleaned at this point.


After all of the above was done, i warmed it up, removed plug from IACV, tryed to adjust idle by the screw, and I notice that when I adjust it, it will raise the idle slightly but then drop back down no matter how much I adjust it out. I havent adjusted it too far out, most i went was a little past flush with the throttle body itself.


So basically, after checking and cleaning and messing with everything possible and eliminating the FITV all together, I still have a 200-300 RPM warm idle and a idle adjustment screw that doesnt effect the base idle at all.



I read a thread on here that someone said "When your idle screw makes no effect then the IACV is bad but I cant remember where I read that" thats just a random opinion so i wasnt just gonna jump on that solution.


Oh and no check engine lights or nothing like that.

Any insight would be very appreciated.

 

bleh

 

One reason the idle screw would do nothing is if the throttle cable is too tight. Turn the key to on and connect a meter set to 20v to the battery negative and the TPS signal wire. The reading should change with the position of the throttle and you can use this when setting the idle to see exactly how much, if any, the idle is changed with each adjustment.

 

I went to go do that tonight and for some reason ( i havent owned the car long so I havent replaced/checked plugs/wires yet) i removed the spark plug wires to find every tube filled with oil, the previous idiot owner didnt install the spark plug tube seals on the VC at all, there was nothing there. So it had been like this since i bought it, and while he drove it as well.


Needless to say I spent a hour or so soaking up/shop vac'ing out the holes as good as possible, replacing the plugs and wires and new vc gasket set. I figured somehow that had to have something to do with the **** poor idle since the spark plug wires were halfway submerged in oil, but still the same deal. Atleast I got that ridiculous issue out of the way so i can move on to fixing this. I spent my whole night doing that making sure everything was corrected from the retardedness.


Ill check out the TPS tomorrow, its still got the factory bolts on it and im throwing no CEL's so i doubt the tps has anything to do with it since it hasnt been moved and seems to work fine anyway.

 

Just so you know, I'm not suggesting that the TPS might have a problem so it doesn't need to be tested. Just that when you adjust the idle screw, watching the TPS reading will let you see exactly how much the screw is moved each time.

 

Since when does the base idle adjustment screw change the tps signal voltage?

 

Since always. The TPS voltage changes with the position of the throttle. If it's at, say, .42v at closed throttle and you began to screw the idle screw downward, the voltage would change to .41, .40 and so on because the throttle plate is closing further. Unless your TB works differently than a stock b16 one does. Normally the idle screw props the plate open.

 

hmm strange. does the car drive strong? i mean, is this the only problem with how the engine is running?

 

you're off track on this one. the idle screw i think he's referring to is the base idle adjustment screw which is a philips head and is on the back of the throttle body. adjusting that doesn't move the tps at all, all it does it open up the idle some more...basically like a controlled vacuum leak. the screw you're thinking of is the one on the actual throttle itself and it's really small. btw, there's a reason u can't adjust the base idle...it's because our ecu's control timing. when you lower the idle, timing changes so the ecu corrects it. there's a procedure in the manual on how to adjust it. you can first do it by disconnecting the iacv plug and then raise the idle up to about 500 while it's warm. when u plug the iacv back in it should go up to about 800. if you're still off, jump the check engine light plug and throw a timing light on. then you can go about getting your distributor to have proper ignition timing and then move the idle screw. there's a lot of factors that go into idle.

 

It runs very well in every other aspect except for the idle. Runs "strong", doesnt burn/leak/smoke oil or any of that jazz. Motor supposibly had 35-40k from the engine distributor and ive had the VC off and it looks very damn nice so im convinced anyway, or atleast its been took well care of before I owned it.


Yes I was referring to the base idle adjustment screw, like you said.


Ive noticed that alot of the times during the day it idles where the needle sets on the stop (on a 92-95 civic cluster, so thats below 500) and sometimes later in the night it will idle dead on 750-800 like it should. Then the next day itll be right back on <500. Its really weird.

 

also to add, every idle adjustment ive made was warm with the IACV disconnected. If i close the idle screw all the way, and disconnect the IACV, the engine dies. If I open it up 1 full turn and disconnect it, it stays running. If I then turn it out 1 more full turn it raises slightly again, but no more after that. 2 turns out is as much as i can move it with it effecting the idle at all, it will not raise anymore and it still doesnt raise to the point of where its supposed to be at with the iacv disconnected. However if I turn the screw in, it will lower it to the point of it cutting off if i closed it all the way.


So if the screw isnt doing **** with the IACV disconnected, theres got to be a reason for that alone, correct? Could this be what you are describing perseverance with the timing? Everytime i think of adjusting idle i think to jump off the 2pin brown connector but then i remember to only use that for setting timing.


Im a bit confused with the whole ordeal.

I did swap the throttle body the other night just to make 100% sure with a 65mm professional products i had, just to make sure there wasnt something i wasnt quite seeing, like possibly gunk in one of the airways leading to the iacv or something of that nature, but it helped nothing.

 

Replaced the IACV out for one off my brothers car which was known to be working, problem still persists.

 

maybe try putting a new FITV on it? did you do what perseverance said? that is true that you should jump the 2 pin connector before adjusting the idle screw.

 

Havent yet, been busy about to get started on it in a bit and see if i can come up with anything else.

I thought the only time you needed to jump the 2p connector was when you adjust the timing? Distributor hasnt moved or been removed since ive owned the car so i know the timing cant be off, i do have a timing light but if i cant get it to idle at 750+/- 50 then theres no point in even checking the timing is there?

 

Tryed the method with the 2p connector jumped, nothing different by doing that.


Tonight I was setting in a line of cars and it started hunting idle from 800rpm-1300rpm. This **** gets weirder and weirder. I tapped the throttle slightly and it did the hunt once more and then dropped back down low...

When im driving if i put it in neutral to coast to a stop, it will stay on 800 rpm's the whole time im coasting, and ill stop and its fine but then it will drop down to 500 and under like ive been saying after im stopped for about 2-3 seconds.

 

Think i fount out that there was a small vacuum leak around the fitv from where i reinstalled it causing the hunting.

I add that I just the other day replace the spark plugs, wires, fuel filter, changed the iacv for another, tryed 2 diff fitv's and tryed the fitv blockoff, and tryed another throttle body.

 

and after all that....it runs properly now?

 

No it still doesnt, i just meant i fixed the hunting idle that started out of no where. It still idles really low. lol

 

JUST FOR SEARCHING / INFO PURPOSES IM POSTING AGAIN. THE ISSUE HAS APPEARED TO HAVE BEEN SOLVED.


Since the b16a p30 oem intake manifold has the wide bolt style IACV, and they seem to be harder to locate, i took a look at my AEBS manifold I had setting waiting to be used on my n/a build. I noticed it used the closer bolt style ones, the ones you see on most everything. So I said screw it, i had nothin to do that afternoon and I had a close bolt style iacv in my garage so I decided to just swap my throttle body / IM and put the new iacv on the new manifold. So i replaced the oem b16 and oem p30 manifold with a AEBS manifold and professional products 65mm throttle body, and the new style IACV and it idles perfect now. Since I swapped all 3 items at once including a new intake manifold gasket, i cannot say 1000% certain it was the iacv, but its aparent it pretty much was, even though i had no CEL, it was cleaned out and appeared to be working properly, aparently that wasnt cutting it. I used the FITV from the b16 throttle body so that had nothing to do with it, even though I knew already that couldnt be causing the problem. Figured i'd add that just for more info.


READ BELOW, ISSUE ACTUALLY HASNT BEEN SOLVED. I JUMPED THE GUN.

 

cool. glad you got it sorted out.

 

I WAS KIDDING I GUESS, ****. I thought it was gone, but it wasnt.


Ok so when i put the AEBS mani and the throttle body on there, i was doing it just to see what happened with the idle, and just for the hell of it really. I was saving them both for my lsvtec build. Ok so it idled around 1k when warm with the new IM/TB/IACV installed. Then all of a sudden, it wanted to idle at 1500 when warm, and thats with the idle screw all the way screwed in. So i was like ok what the hell has to be something to do with the throttle body being open more than the stock one or something, possibly sticking, a small adjustment different.


So tonight, i swapped the throttle body back out for my stock b16 one, i cleaned the ever living **** out of the stock one before installing it, making it internally/passages spotless. I left the same small bolt style IACV that i installed when i installed the aebs mani on there, but just put the stock b16 throttle body back on, also removed the fitv again just to get it out of the way really since i had a blockoff plate made for it already.



NOW, it wants to idle low as **** again. So the only thing that made it idle higher was the other throttle body, and it made it idle way high even with the idle screw all the way shut. So im guessing the other throttle body butterfly stop was just slightly further out than the stock b16 one, keep in mind that my stock b16 one still has the yellow paint on it from the factory and lines up with the markings, so the butterfly has never been touched, and has also been cleaned vigorously. This is the 4th iacv ive used on the car, FITV removed and installed, all the same ****.



So what in gods name could possibly be causing this? Ive had the intake manifold on/off 3 times, new gasket everytime, 4 different iacv's, cleaned throttle body out the ***, removed the fitv completely, reinstalled it and adjusted it/cleaned it, removed it again... So the FITV/IACV/throttle body/IM are completely out of the question, theres no way in ****. Theres also been a new fuel filter, spark plugs, and wires installed. Theres also never been a CEL with any of the installed parts, and everythings been cleaned/or clean prior to install. The only thing different between the two throttle bodys that could possibly even make a difference is theres a different TPS installed on each one, but they are both calibrated dead on and work fine.


WHAT ELSE could possibly cause this. The damn car still runs flawless when not idling, no spitting or sputtering, no smoking, no hesitation, great MPG, blah blah blah.

 

Too much reading to do here so forgive me if you've already checked: Ignition timing, cam timing, and excessive slack of the timing belt. Id also do a compression check just to somewhat verify you're working with a mechanically normal functioning engine. Id also temporarily disconnect the brake booster to verify an absence of an external vac leak.

 

Ignition timing, dead on @ 16 BTDC. Cam timing, stock cam gears. Timing belt is correct tension, cam gear marks line up when @ TDC on crank. I havent done a compression test because ive felt no need since it does run really well, and burns no oil, leaks no oil, etc. I will however do a compression test tonight or tomorrow just to 100% verify. I'll check the brake booster line though just to make sure of that as well. Ill report back with compression numbers and what happens with the booster disconnected / line plugged off with a vaccuum cap

 

Did a compression test tonight. Remember completely bone stock B16A from jdm-online.com, estimating 50-75k on the engine, max. Internally the head looks brand new almost, its been took great care of.


Numbers are almost perfect.

Cylinder 1: 225
Cylinder 2: 220
Cylinder 3: 220
Cylinder 4: 225


Tested voltage @ the IACV connector. With positive terminal to yel/blk wire on connector and negative terminal to body ground, with the key ON, i get 12.2v. If I put the positive terminal to yel/blk and negative terminal to the blue/yel wire on the connector, i get 11.37v. Thats normal and checks out fine, correct?


Plugged off brake booster line with a cap, no effect on the low idle.

 

Just double checking here, but when you disconnect the IACV while the engne is running, is there a change in idle speed? Does the CEL come on?

Im racking my brain trying to think of a culprit..

edit: after reading your previous posts more thoroughly, it appears this problem started right after you adjusted the FITV to solve your high cold start idle correct? After a bunch of tests you decided to reinstall an FITV and the problem still persisted? You also mention a change of the throttle body gasket. Which gasket did you use (there are tons of configurations/cutouts in the gaskets available..not all B series throttle body gaskets are the same)? Hopefully your new gasket matches whaichever setup you are testing (i.e. if using an FITV, be sure to use a TB gasket with the proper cutout for FITV air flow thru the throttle body). Dont forget the FITV needs coolant hoses attached, the IACV doesnt matter either way. From your descriptions of the problem, it sounds like you know what you're doing but we cant overlook the simple stuff..so regarding ign. timing, you are aware of what the timing marks represent and which cylinder #1 is? Keep in mind, checking/adjusting the timing must be done with the engine running at the proper idle speed.