flood

D16Y8

The CEL came on with code 14 (IACV) the other day. I was cleaning out my IACV in hopes that I dont have to replace it. I was able to reset the ECU and the light hasn't come back on. However it now jumps the idle around when you push in the clutch and cruise to a stop. 1000-1700rpm over and over. Not every time either.

So I cleaned it out put it back on, same thing. Cleaned it again. Same thing.

It seems as though its a pretty simple device. A coil, plunger and ECu sends voltage to it in order to control it. So is the IACV really bad or is the ECU sending a signal causing it to jump around like that?

Also what is the normal operation of the idle? When I am coasting to a stop with the clutch in the idle goes to 1500rpm, then once the car is stopped it drops to 1000, then to ~700.

I dont remember it staying at 1500rpm when cruising to a stop before this started, but I can't remember.

And another question. What is the purpose of the coolant lines running to the IACV? IS that for the cold idle? the newer version of the FITV?

ralphie14

Sometimes it will do that for a little while, how long did you wait before you tried to reclean the thing?

sicones

the coolent lines are just for letting the car heat up faster in the winter, your car dosent have a FITV the fast idle is controled by your IACV and on the 99-00 the fast idle is controled by a fuel injector air system

flood

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ralphie14 &raquo;</TD></TR><TR><TD CLASS="quote">Sometimes it will do that for a little while, how long did you wait before you tried to reclean the thing?</TD></TR></TABLE>

A week inbetween. It only does it occasionally.

I know that the ECU can control idle based on a few various inputs from the PS pump, AC and electrical load. I was just wondering if perhaps its not actually the IACV that isn't working 100%.

I am most likely overthinking it. I may just replace the thing and see what happens. Bad thing is that the IACV is expensive. Saw some on ebay but they are all dirty with cooland and crap. Mine looks better

Still doesn't answer the question: why do IACVs cause RPM to jump around when they go bad?

ralphie14

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flood &raquo;</TD></TR><TR><TD CLASS="quote"> Still doesn't answer the question: why do IACVs cause RPM to jump around when they go bad?</TD></TR></TABLE>

Because the sensor is not sending an accurate reading to the ECU. With a bad reading the ECU is not going to know what is going on and will try to compensate for the reading that it is receiving.

IHateJDM

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flood &raquo;</TD></TR><TR><TD CLASS="quote">Also what is the normal operation of the idle? When I am coasting to a stop with the clutch in the idle goes to 1500rpm, then once the car is stopped it drops to 1000, then to ~700.
</TD></TR></TABLE>

1500 cold, 750 warm

civic_driver

the iacv doesn't send anything to the ecu... the ecu controls the iacv and the ecu gets its measures from the map, tps sensors and so on

it probably gets clogged internally, wires corrode, wrong readings, weather effects, problems elsewhere not essentially related to the EACV cause the ECU to do stupid things... first way to test it is with a multimeter... if everything is okay there it's either an internal IACV problem or a problem elsewhere... at this point i would replace with a brand new one and if still doesn't fix problem, it's a problem elsewhere... or maybe that's how it SHOULD act based on the current conditions but you never experienced it before... of course we want things simple..

many times, the FITV is to blame for irratic idle but as the IACV ages, it starts getting clogged up internally due to garbage going through it...

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sicones &raquo;</TD></TR><TR><TD CLASS="quote">the coolent lines are just for letting the car heat up faster in the winter, your car dosent have a FITV the fast idle is controled by your IACV and on the 99-00 the fast idle is controled by a fuel injector air system</TD></TR></TABLE>

The coolant lines into the IACV (which is what he asked) are there to "warm up" the plunger inside the IACV. As the car is cold, the plunger is open more, allowing more air to bypass the throttle body and thus effectively raising idle. when the car warms up, the coolant heats up the plunger and thus causes it to close. This reduces vac loss and lowers idle. Its the same concept as the FITV, only it can also be electronically controlled via the ECU to compensate for things such as increased electrical load, etc..

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ralphie14 &raquo;</TD></TR><TR><TD CLASS="quote">

Because the sensor is not sending an accurate reading to the ECU. With a bad reading the ECU is not going to know what is going on and will try to compensate for the reading that it is receiving.</TD></TR></TABLE>

No.. There is no "sensor" in the IACV. Its a solenoid... by applying various voltages, you can control how wide it opens the plunger. The ecu sees nothing from the IACV. Well, I shouldn't say it sees nothing, because it does check for ground and can thus throw a code when the plug isn't plugged in... anyways... It SENDS voltage to open the IACV to adjust idle based on readings from other sensors. If it cannot correct the RPM to an "acceptable" range, then it will toss a code because it assumes there is a problem with that circuit. You people have a horrible habbit of using MIL codes as gospel. The ECU can only do so well in determing the problem. It does not always mean that is the problem... So don't assume the IACV is the problem until you have tested it. It could very well still be good and not the cause of your problem..

flood

Good explanation.

I kind of wonder if the IACV is the problem or not. It was "hella" dirty, but that doesn't mean its broken.

I almost wonder if the ECU is seeing something incorrectly and adjusting idle via IACV to compensate.

For example in a perfect world:
Front Defroster is turned on, which in turn activates the AC.
AC compressor sends signal to ECU that its on (load).
ECU sends signal to IACV to increase throttle to compensate.
Idle doesn't increase, ECU throws IACV error.

So now lets say the AC sensor is sending false signals.

AC compressor sends signal to ECU that its on (load).
ECU sends signal to IACV to increase throttle to compensate.
AC compressor stops sending signal
ECU sends signal to IACV to decrease throttle
AC compressor sends signal to ECU that its on (load).
ECU sends signal to IACV to increase throttle to compensate.

This would give you a fluctuating rpm, this is the type of loop that I think is occuring and also wouldn't throw the CEL because everything is "working". I have read a few threads about the IACV where they replace it and the same problem occurs.

A good Honda scanner would come in handy. I could monitor all the ECU sensors while driving it.


Modified by flood at 12:54 PM 12/15/2005

flood

Checked helms.

When idle speed is out of spec and the scan tool does not indicate trouble code check the following:

Starter switch signal
AC signal
ALT FR signal
Brake switch signal
PSP switch signal
Clutch switch signal


If the above items are normal, substitute a known-good IAC valve and readjust idle speed.

If the ilde speed still cannot be adjusted to sepc and you get no code after IAC valve replacment, substitue a known good ECM/PCM and recheck. If symptom goes away repalce the ecm/pcm.

vtakvtrak

I have the same problem, for some reason I think its my p28 chipped eriks racing ecu sending the wrong signal...

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vtakvtrak &raquo;</TD></TR><TR><TD CLASS="quote">I have the same problem, for some reason I think its my p28 chipped eriks racing ecu sending the wrong signal...</TD></TR></TABLE>

A lot of times, the chips people are using will cause the idle to bounce around. Its not any fault of the IACV or anything else... Its simply the chips people are using that run either way too damn much fuel, incorrect ignition timing in that section of the map, or a combination of the two. The problem is people buy these "chips" from ebay and other vendors and then just run them as is. This is a big no no if you ask me. Every engine is different and thus has different needs. There is no one magical set of fuel/ignition tables for every engine.

sicones

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hybrid93Eg &raquo;</TD></TR><TR><TD CLASS="quote">

The coolant lines into the IACV (which is what he asked) are there to "warm up" the plunger inside the IACV. As the car is cold, the plunger is open more, allowing more air to bypass the throttle body and thus effectively raising idle. when the car warms up, the coolant heats up the plunger and thus causes it to close. This reduces vac loss and lowers idle. Its the same concept as the FITV, only it can also be electronically controlled via the ECU to compensate for things such as increased electrical load, etc.. </TD></TR></TABLE>

I don’t think an electronic solenoid IACV would have properties of a heat sensitive plunger the IACV is solely electro-mecanical in nature and does not respond hot and cold can you please explain your self further do you have any facts or evidence stating this, I would really like to know.
Thanks

flood

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sicones &raquo;</TD></TR><TR><TD CLASS="quote">

I don’t think an electronic solenoid IACV would have properties of a heat sensitive plunger the IACV is solely electro-mecanical in nature and does not respond hot and cold can you please explain your self further do you have any facts or evidence stating this, I would really like to know.
Thanks
</TD></TR></TABLE>

Well when I took my IACV off (cold) it was closed 100%.

I don't have a clue as to what the coolant lines in the IACV are for.

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sicones &raquo;</TD></TR><TR><TD CLASS="quote">

I don’t think an electronic solenoid IACV would have properties of a heat sensitive plunger the IACV is solely electro-mecanical in nature and does not respond hot and cold can you please explain your self further do you have any facts or evidence stating this, I would really like to know.
Thanks
</TD></TR></TABLE>



Looking at this image I would say you are right and I was wrong in the function of the coolant lines. The only logical explanation I can think of is similar to the function of passing coolant through the bottom of the tb... To help slightly heat the incoming air for better atomization...

EE_Chris

When you add air into the manifold of a speed-density metered fuel injected engine, the idle raises. Nothing new here. However the Honda ECU uses a fuel-cut-on-decel strategy to save gas and cut emissions.

When you're coasting down a hill and lift off the gas, the fuel injectors are cut off. The only inputs the ECU uses to accomplish this is a) engine rpm and b) TPS input. When engine speed is above 1100rpm and the TPS shows the throttle is closed, the fuel injectors are cut off.

Well if you've got a faulty IACV (or vacuum leak) allowing air into the manifold, which increases engine speed, this fuel cut strategy will be activated (moving or not). So the loop is really the ECU cutting off the fuel injectors, which causes engine speed to decrease. It then drops below a threshold, ECU cuts injectors back on and in addition to the air being supplied by the stuck-open IACV, engine speed raises and the cycle continues.

Hybrid also pointed out the custom fuel and ignition curves and that's a probable cause too if you're running a non-stock program.

Coolant lines are ran to the IACV to keep it from freezing and sticking. It has nothing to do with any function like the FITV servers.

What is your idle set to if you unplug the IACV while the engine is fully warmed?

amckee

I agree. Base idle MUST be set properly for the IACV to work properly. Remember, it is meant to increase the RPM of the engine when cold or under load at idle such as PS or A/C. It was not meant to lower the idle as a result of a missadjusted idle or vacuum leak. You know how you read some threads and people will say that when you unplug the IACV sometimes the idle increases and sometimes it decreases. Well, if it increases when someone unplugs there's, that's a good sign of a vacuum leak or a missadjusted idle.

flood

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EE_Chris &raquo;</TD></TR><TR><TD CLASS="quote"> What is your idle set to if you unplug the IACV while the engine is fully warmed?</TD></TR></TABLE>

Fully warmed all accessories off (IACV unplugged) its ~500rpm going off the tach in the car.

I pulled the air cleaner to intake hose and looked in the intake. the butterfly valve was fully closed. The throttle cable has just a bit of slack. I plugged the PCV valve hose adn the rpm dropped jsut a slight bit and raised when the hose was released (replaced PCV valve about 10k mi ago). Rechecked base idle (~500rpm). Listened for vacuum leaks and didn't notice anything.

everythign there checked out fine.

When fully warmed it idles fine, except when I am driving along say ~50mph and push in the clutch. RPMs drop to 1000, then go up to 1500rpm and usually stays there untill I stop. (is this normal?)

when I stop the idle drops to 1000 then to 750 pretty quickly. If I tap the throttle just a bit from a complete stop, it goes up to 1500 then back to 1000, then 750. (again is this normal?)

Now sometimes when going 50mph I will push in the clutch and the RPMs go down to 1000, then 1500 then 1000 then 1500 then stablize at 1500 untill I stop. once stopped it does the 1000 to 750. I know the bounce between 1000 and 1500 isn't normal.


Modified by flood at 1:55 PM 12/16/2005

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flood &raquo;</TD></TR><TR><TD CLASS="quote">

Fully warmed all accessories off (IACV unplugged) its ~500rpm going off the tach in the car.

I pulled the air cleaner to intake hose and looked in the intake. the butterfly valve was fully closed. The throttle cable has just a bit of slack. I plugged the PCV valve hose adn the rpm dropped jsut a slight bit and raised when the hose was released (replaced PCV valve about 10k mi ago). Rechecked base idle (~500rpm). Listened for vacuum leaks and didn't notice anything.

everythign there checked out fine.

When fully warmed it idles fine, except when I am driving along say ~50mph and push in the clutch. RPMs drop to 1000, then go up to 1500rpm and usually stays there untill I stop. (is this normal?)

when I stop the idle drops to 1000 then to 750 pretty quickly. If I tap the throttle just a bit from a complete stop, it goes up to 1500 then back to 1000, then 750. (again is this normal?)

Now sometimes when going 50mph I will push in the clutch and the RPMs go down to 1000, then 1500 then 1000 then 1500 then stablize at 1500 untill I stop. once stopped it does the 1000 to 750. I know the bounce between 1000 and 1500 isn't normal.


Modified by flood at 1:55 PM 12/16/2005</TD></TR></TABLE>

It all seems normal to me. Perhaps the IACV response might be a touch slow as to why the slight fluctuation when rolling... but my idle has also done what you describe when rolling and coming to a stop. Thats the way it should be.

94eg!

iTrader: (2)

If it hasn't been discused already, I will add the following:

On my OBD1 civic, every time you clear the codes by pulling the memory fuse, the computer must start from scratch. The ECU adjustes pre-programed fuel & timing maps by way of the O2 sensor (and other sensors too). It must re-adjust all those OEM values to get the car to run properly again. This takes time, and usually results in a "bobbing" idle. My car's idle will bob up and down every time it idles once it's warmed up. This will go on for a few days until it gets re-adusted.

I think that your modifications, climate & elevation will be the major determining factor as to how long it takes to adjust. The further from the OEM values you are, the longer a period of time your car will drive funny...

flood

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote"> I think that your modifications, climate & elevation will be the major determining factor as to how long it takes to adjust. The further from the OEM values you are, the longer a period of time your car will drive funny...</TD></TR></TABLE>

Agreed. I figure I will try it for a while and see what I come up with.

5000ft ASL, I would say its pretty far from OEM values.

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote">If it hasn't been discused already, I will add the following:

On my OBD1 civic, every time you clear the codes by pulling the memory fuse, the computer must start from scratch. The ECU adjustes pre-programed fuel & timing maps by way of the O2 sensor (and other sensors too). It must re-adjust all those OEM values to get the car to run properly again. This takes time, and usually results in a "bobbing" idle. My car's idle will bob up and down every time it idles once it's warmed up. This will go on for a few days until it gets re-adusted.

I think that your modifications, climate & elevation will be the major determining factor as to how long it takes to adjust. The further from the OEM values you are, the longer a period of time your car will drive funny...</TD></TR></TABLE>

The ECU makes adjustments to long term fuel trims, NOT to the ignition tables. The stock tables should not be off enough to cause any sort of 'bobbing' at idle with a reset ecu either. If they are, then you have a pretty extensive mod list or some thing else going on either allowing additional air flow or restricting air flow. If its taking your car several days to "adjust" itself to correct idle, something is wrong.

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flood &raquo;</TD></TR><TR><TD CLASS="quote">

Agreed. I figure I will try it for a while and see what I come up with.

5000ft ASL, I would say its pretty far from OEM values. </TD></TR></TABLE>

Thats what a barometric pressure sensor is for..

flood

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hybrid93Eg &raquo;</TD></TR><TR><TD CLASS="quote">

Thats what a barometric pressure sensor is for.. </TD></TR></TABLE>

True