Honda Civic 1996 - 3 Wire IACV Voltage Reading - KOEOff/KOEOn

[Hassan1991]

Also i'm assuming iacv to be okay here. Between have you check the resistance between terminals of iacv?

[Xulfiqar]

make sure the IACV is good itself - then trace its wires to ECU for good connectivity (no corrossion etc) - then check if its getting any command from ECU, use a DMM with a Hz setting or use an oscope as its very finely divided time base measurement.

[hasankhurshid29]

You may have some leak which is causing high idle. Also did you mess around with throttle idle air screw?
If its too loose, it will let too much air and iacv will not be able to control idle.
Like when I cleaned throttle body and sprayed carb cleaner in IACV port last week, my idle wasn't being able to controlled by iacv. So i have to close throttle idle air screw to get IACV to control my idle.

Simply this means if too much air is already bypassing the IACV will sit at 0% as even if its fully closed, the idle is still high

I am also using Hondash
My IACV is 2 pin one

[shabbir.1]

i have cleaned the throttle body 2-3 times. cleaned the iacv as well. everything is squeaky clean. the iacv is rotating freely, no carbon buildup at all. cleaned it really good.

How did you clean the valve?

I mean to say that the 3 wire/ Rotary type IACV can't be cleaned thoroughly in situ due to its installed position unless removed from the throttle body.

Spraying cleaning agents inside the TB dislodges carbon buildup and actually accumulate the same inside the cavity where the IACV spindle rotates to control the amount of air. Though it may apparently look clean and moving freely for the time being, the movement actually becomes further sticky.

While there can be better ways to do the necessary cleaning, but the method I adopt is to remove IACV from the TB, unscrew the plastic actuator body to get access to the spindle or whatever you call it. Pull out the spindle and then thoroughly clean it along with the cylindrical cavity machined inside the valve with carb-cleaner and wipe it clean with a rag without scratching anything. Reassemble and attach it back to the TB, it should work flawlessly for much longer period of time.

You may need not to remove the coolant lines if you can find a better position with enough working space while leaning down in the engine-bay for extended time.

[Xulfiqar]

You also need to add some oil to the valve as its a zeolite type bearing.

[nfssaad]

resistance to be checked.

sometimes the car remains at fast idle,

sometimes the rpm keeps fluctuating between 800 and 1400, ie engine is hunting

turning on ac or headlights, does have some effect on the iacv, the rpm fluctuate and reduce a little.

[nfssaad]

cleaned by complete throttle body removal.

remove the iacv, use a tooth brush and petrol to clean the valve part.

i am unable to remove the plastic part due to completely stripped and rusted screws. didnt use more force to avoid any damage.

the other end has a plastic cap with two small screws, which has a stopper of some sort to prevent the iacv rotating full round. checked the spindle rotation from that end, spindle moves freely. it would appear to have a magnetized part, so it rotates in two steps.

if the spindle is at complete 180 degrees from is original position, the engine starts and immediately idles at 4000 rpm.

if at its original position is stays at 1300-1400, and fluctuates.

i am not getting any error codes

[nfssaad]

the throttle idle air screw is uses a flat head screw driver and has a pointed end?

if so, its fully closed tight.

[Hassan1991]

Iacv itself can be bad.
Remove the connector from iacv and see if car dies.
Have you adjusted the idle screw? It should be at its original position.

[shabbir.1]

Noted Sir, will try next time.

[shabbir.1]

i am unable to remove the plastic part due to completely stripped and rusted screws. didnt use more force to avoid any damage.

Apply WD40 and use a PH2 size Phillips head screwdriver, use a mallet to hit and force the driver bit firmly inside the screw head, then use full force to rotate it and replace the screws with new ones.

the other end has a plastic cap with two small screws, which has a stopper of some sort to prevent the iacv rotating full round. checked the spindle rotation from that end, spindle moves freely. it would appear to have a magnetized part, so it rotates in two steps.

if the spindle is at complete 180 degrees from is original position, the engine starts and immediately idles at 4000 rpm.

You need not to remove this plate. The spindle is magnetically coupled with the actuator encased in plastic body. The other side has a stopper dampen with a coil spring and positions the spindle precisely, fiddling with it may affect the rotating angle of the spindle.

As I said earlier, you only need to remove the actuator body (connector side) and do the necessary cleaning.

Picture courtesy: https://www.instructables.com/Replacing-an-idle-air-control-valve/

In resting position the spindle will only show a small slit (around 2mm) for air to bypass. If you move it further to open the slit and release, it should return to its original position.

[shabbir.1]

the throttle idle air screw is uses a flat head screw driver and has a pointed end?

if so, its fully closed tight.

Picture Courtesy: http://civic-eg.com/forum/viewtopic.php?p=206306

Idle adjustment screw aka BISS (base idle set screw) is shown here, it is used to set the base idle value of around ~450 RPM (mostly D series engines) when the electronically actuated valve (as IACV in this case) is not functioning or deactivated.
If it is already tightly closed and still engine is idling high, believe me your engine has vacuum leaking issue somewhere.

As @Hassan1991 suggested above, please remove the IACV connector when the engine is running to confirm whether RPM drops suddenly or not.

[Xulfiqar]

sometimes the BISS O ring gets brittle and breaks, this causes an uncontrolled air leak as it can unscrew itself from vibration, in the days of ye-olde (when I had complete dark hair) and I was riding shotgun with the posse, I would dab some silicone on it to hold it steady,

After some maturity (read as buying O ring kit case) I replaced the O ring on it.

[nfssaad]

the oring was compressed, but still flexible..

[nfssaad]

disconnecting iacv has no effect... car starts up as well.

suspecting a leak now... but from where

[nfssaad]

it works exactly like that. the slit is at 2mm approx.

the iacv is a slightly dirty version of the iacv pictured on the right.

[Xulfiqar]

Use carby spray to find it. Or smoke it.

[Hassan1991]

You can hear if Iacv leaking air by taking the air filter pipe off. It can be stuck open.
Yes do check leaks as sir Xulfiqar said.

[shabbir.1]

I have had this unique experience to come across at least two such cases where an oversize (big O/D or fat O-ring) was used with the screw, thus inhibiting its actual function. It won't allow any air, no matter how much loosen, unless totally removed.

[shabbir.1]

I suspect, air could be leaking in from the plate-end of the IACV that you have already opened for cleaning purpose. Apply a dab of silicon where the plate makes contact with the valve body and try not to open it next time. You have to access the spindle from the actuator/ connector side, if required so.

Other possible reasons can be;

a. leaking gasket between TB and the IM plenum
b. improper adjustment of throttle stop screw or more than recommended gap between the throttle plate and the orifice at full closed throttle
c. improper adjustment of throttle cable (too much tension)
d. leaking vacuum pipes e.g., vacuum pipe for brake booster/ PCV connection/ FPR etc.

To check whether the valve is stuck-open and possibly leaking air internally, remove the filter box along with the intake duct. Place your thumb on the inlet hole inside the TB for the IACV, and check whether the RPM drops as you block it. If the engine stalls you are at the right spot, the IACV is sticky and needs proper cleaning or might be defective otherwise.

Picture courtesy: https://www.b-parts.com/auto-parts/engine-transmission/throttle-body-honda-civic-vi-aerodeck-mb-mc-14-16v-mb8-ts006-1998-1999-2000-2001-4476846

The upper round hole is for the BISS air bypass and lower elongated opening is for the IACV inlet port, if you can't place your thumb properly to block it find something other like a piece of rubber sheet etc.