Ok, I have the classic surging idle. Please help me out Honda-Tech, I don't know what else to do. I have a b18c5 in a 94 Civic hatch. I have always had to have the idle screw turned all the way in to avoid the surging idle. This past week I however it started doing it even with the screw all the way in. If I start the car from cold and let it idle until it is warm it will idle fine right at 800 rpms. As soon as I drive it and come to a stop sign it starts up.

So far I have bled the coolant, cleaned the IACV, Cleaned the Throttle Body, loosened the throttle cable, replaced the PCV, checked for vacuum leaks (there are none, i checked with a smoke machine). I don't know what else to do.

I have taken notice that when the engine is hot there is still suction at the IACV hole in the Throttle Body, shouldn't the IACV stop working when the engine reaches operating temp?

Could this be an ECU problem?

Help me out guys, I really need to fix this problem and I don't know where to go from here

 

the IACV works at idle to bypass the TB and pull air into the engine so it will stay running.

It sure sounds like classic IACV problems to me. Even though you've cleaned it and can hear the air rushing around it at idle it could still be the IACV - mine was flakey, it would only open half way. (same swap, 92 hatch)

it could be your idle settings - if it's set to low the ECU wil see the engine die down and rev it a little to keep it running then let it try to idle... and back and forth.
there is also the opposite that can happen, if your AICV is set to high (chipped ECU) then the idle will pull up till the ECU sees it to high and pull it back down... repeat.

Which ECU are you using with the c5? chipped? where did you have it tuned? (purchased chips are virtually worthless on the C5)

 

I have to have the idle set that low or it will do the surging all the time, even before it is warm.
I honestly don't know what ECU I am running, I bought it on ebay before I really knew what I was doing and it was listed as an OBD1 P73 which I know doesnt exist. It is said to have a Skunk2 chip. It has always seemed to work fine, so I never bothered with it.

Another thing is that I hooked it up to a scanner today and it told me it was running on open loop at an idle, the only time it switched to closed loop was when I revved it pretty far up and as the RPMs were dropping it quickly switched to closed loop and then back to open. I don't know if this would have anything to do with it or not.

 

I hope you're not running open loop all the time on an untuned chip.
either way pick up a burner and read the chip you're running. Then pick up a copy of crome and set everything yourself.

you'll want a wideband to tune the car right, but it shouldn't be required to get this working right.
You can also find someone in your area to tune the car, worth the money 10 times over.

 

I really don't know anything about what you just said. I think I might just get an ECU from Kenji and hopefully that will fix all of my problems. What do you think about that?

 

Does anyone else know what could be wrong with my idle? Do you think it's a bad IACV or do you think an ECU will cure this?

 

I had the same problem on my b16 so I bought a new IACV from discount auto parts and still had the problem so I took the IACV back to discount got my money back then I went to the honda dealer and bouight a IACV from them and no idle issues since

 

When I did the swap I bought a used IACV from either this site or ebay, so I am def not ruling out the IACV. I just don't want to spend how much for a new one from Honda if mine is working fine. Is there anyway to test it? Is there supposed to be suction at the IAC hole in the throttle body when the engine is hot? I was always under the impression that the IACV only controlled the idle when it is cold and then stops functioning after it is warm. I still have suction when it is hot.

 

When the motor is warm, unplug the IACV: What does the idle drop to?

Does you motor have an FITV mounted on the throttle body?

 

No, I don't have a FITV. When I unplug the IACV the idle drops to about 500 RPMs

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ITR EG &raquo;</TD></TR><TR><TD CLASS="quote"> I was always under the impression that the IACV only controlled the idle when it is cold and then stops functioning after it is warm. I still have suction when it is hot.</TD></TR></TABLE>No the IACV functions cold and warm, when the car is cold the IACV keeps the idle high until warmed up and when the car is warm it maintains idle...Buy 1 from honda it worked wonders for me,mine used to surge up n dn when warm and just idleing (drove me crazy) bought the honda IACV and no more problem idles like a champ and I have stage 2 cams

 

I don't want to just throw parts at this and waste money, if it needs an IACV I will surely buy one from Honda. But I need to be pretty certain that that is the problem before I buy one. Any more input?

 

Does anyone have any ideas?

 

Well, the fact that you have the idle air bypass screw all the way in sort of indicates something wrong, like a vaccum leak somewhere, since you're having to compensate for that leak by turning that screw all the way in.

Perhaps it could be the ECU - certainly not unheard of for a chipped ECU like that. Can you get a stock ECU and try that?

 

It doesn't have a vacuum leak, I have checked it a few times with a smoke machine. It def. acts like a vacuum leak but I can't find one. I don't have a stock ECU I could try. A friend has a GSR in a hatch that has a chipped ECU that idles fine. Do you think I could try that, or won't it work because it's a GSR? Thanks for all the help guys, any more suggestions?

 

any more ideas?

 

anyone?

 

for an idle check only the P72 should be ok.

where is the ignition timing set to?

 

Timing is set to stock specs, would this affect the idle at all?

 

So last night I hooked by friend's P72 up to mine. It didn't surge, but it idled really high. Then we hooked mine up to his car and it idled really low until it was warm then idled perfect. So then I hooked mine back up and the surging started back immediatly. Usually it will idle fine when started, even when its warm, but as soon as I drive it and stop for the first time it starts up. This time it did it as soon as I started the car. Also a check engine light came on. I haven't checked the code yet, but I have a suspicion of what it is. I had some problems with broken wires at the ECU. I soldered about 5 of them because they were broken. I think there must be a broken wire for the IACV that was causing the idle and now that I moved the wires around it broke off completely and set the light. Does this seem like a decent theory? I don't have time today, but I am going to check it out tomorrow.

 

I love how people conviently leave out details they feel might not be pertinent to the problem at hand.

Yes, having broken wires at the ECU (which you repaired) might just mean there are more you haven't. You should get the code though.

 

I'm gonna get the code tomorrow. And I didn't leave out details. I repaired those wires 3 years ago and had not had a problem since. It did not even cross my mind that there could be a problem there until it acted the way it did until after I swapped ECUs. If I had considered that before or even remembered that I had repaired the wires I would have mentioned it, I had just never considered it before.

 

I think if those wires were bad before, you would have gotten a cel right away, and your ecu wouldn't be able to do anything with your idle, let alone rev it up and down. It would have been really low, just like if you unplugged the iacv. I'm in the exact same boat as you right now, with the annoying revs. I figure I have the wrong iac valve, because when I partially blocked the hole in the TB with my finger, it idled normally. No revving up and down after cracking the throttle. So I just cut out a piece of metal from a paint can, stabbed a couple restrictive little holes in it, and put in between the valve and the IM. Kinda ghetto, but you can't even tell it's there, and I figure I'll replace the valve soon enough anyway. At first I thought it was becasue I had the wrong TB, because I don't have a fast idle valve and my motor is supposed to, (94 ls, I'm not cool enough to have a type r) but now i'm pretty sure it's the wrong iacv..

 

Mine does the same thing when I block off the IACV in the TB it idles normally. It feels like there is a lot of suction there, like more than there is supposed to be. After I check the code and figure out what is wrong there and after I check all the wiring the the IAC, if that doesn't fix it I think I am going to pick up another IACV from Honda and see if that takes care of it.

 

I think I remember the various honda iacvs having different sized air passages, like a calibrated flow restriction. That's basically what I did to mine. I may be wrong though, totally..my iac valve could just be fucked..