I cant get the idle under 2k with the iacv unplugged
after cleaning the carbon there was a slight change, but nothing really noticable.


[Modified by StockYellow, 4:17 AM 3/5/2002]

 

bump

 

im haveing the same problem almost. I thoght i had a bad IACV on my ITR Intake manifold, so I got another one. The problem is still there. With My IACV connected the idle jumps to 2000 rpms and cannot be changed. When trying to drive like this, when i let off throttle the rpms climb and stay at 4k until i get into gear or give it gas. Anyone have any suggestions? also i sprayed all the possible vaccum leak areas with carb cleaner and there was no leaks. When i unplugg the IACV idle is around 600-800 rpms


[Modified by Rattlesn8ke, 2:27 AM 3/6/2002]

 

IF the idle is above 2k with IACV unplugged and idle screw is closed- which port in the throttle body (upper or lower) causes the engine speed to drop dramatically? It should be the lower one. If this is the case- and you are sure you have coolant flowing through the thermal valve- then the valve is not fully closing. You can remove 2 screws (8mm hex/phillips head)on the side of the thermovalve and adjust the ring that the valve seats against. You can turn it with a small flat head screwdriver or sometimes your finger. Turn it clockwise- see if this helps. You can remove just one screw and loosen the other to swing the plate out of your way. On your engine- I am assuming that the IACV is on the backside of the manifold by the firewall and your thermovalve is on the bottom of the throttle body. When the engine is hot- there should be just about zero flow past this valve. What year is your engine?

 

Fixhondas Thanks for the good info here. Are the obd1 and 2 iacv's any different. I switched manifolds last week, on my obd1- p28 brained motor with a d16y8 -obd2 iacv on my car and was getting the surge. So I swaped to the original iacv and adjusted the tps which was a little off and it idles great now. But it got me to thinking that maybe the iacvalves are not all compatible with different ecu's. I dunno maybe you can set me straight.

 

There were two different versions of IACV's used between 96-99: 2-wire & 3-wire types.

All 96-98 Models except D16B5; 99 D16Y5 with M/T:
D16Y5, D16Y8 with M/T use the 2-wire
D16Y5, D16Y8 with A/T, & all D16Y7's use the 3-wire

All 99 Models except D16Y5 with M/T and D16B5:
D16Y8, B16A2 with M/T use the 2-wire
D16Y5, D16Y8 with A/T, & all D16Y7's use the 3-wire

According to the Helms, the procedure for adjusting the idle differs depending on which IACV you have.

 

The 5 speed D16Y8 manifold has an IAC valve- the automatics have a rotary air control valve that needs the corresponding ECU to operate it. If you unplug a RACV the idle will jump higher to above 1,000 rpm. As far as differences in IACVs I am unsure- it wouldn't surprise me if there are differences. I was running a D16Z6 with a 91 Si ecu and injection just fine. When I switched ECUs- the idle went to ****. I don't know if the IACV is calibrated differently or if it has a different valve mechanism. It does seem that the thermovalves are different.

 

Ya thats what I was thinking, because I just couldn't get my d16z6 to idle right with the newer y8 iacv. live and learn, thanks man

 

Thanks, Ill do that as soon as I can get a friend over here.

my car - 1993 honda civic ex coupe
engine - D16Z6

 

I dont have a thermo valve, its on a 98 ITR throttlebody. And the idle only jumps to 2k when the IACV harness is connected. When its unplugged... There is only one hole on the ITR Throttle body and its on top. I plugged it up and it still retaines the idle. Which means the vacuum los has to be from the the throttlebody, and im guessing its the TB gasket.


[Modified by Rattlesn8ke, 11:30 PM 3/6/2002]

 

you can cover the throttle body with your hand- if it still idles- you have a vacuum leak which could be your throttle body gasket or elsewhere.

 

or the manifold gasket??

 

i've tried everything you guys have suggested , but nothing has changed. i changed the thermostat today...that didn't help one bit. any other ideas.................

 

oh, yeah - can you please describe the problem in more detail?

i have this funny feeling we are missing a vital piece of information necessary to provide you with any further appropriate input...

thanks,

im sure a solution will prevail...

t..

 

yeah- please- I have made suggestions and I see no details of what happened when you did any of them.

 

-adjust the ring that the valve seats against. You can turn it with a small flat head screwdriver or sometimes your finger. Turn it clockwise- see if this helps. -

Ok, took off the thermal valve, opened up the front, and I couldnt turn anything on the plunger. It was either completly frozen, or not supposed to rotate.

In the helms manual there says there should be a wax plunger?

The back side I had already fixed, it was completly unscrewd before. Screwed it all the way in and sealed the edges with sealant.

The iacv is on the back of the intake manifold.

also, on the iacv. There is a screw that has 5 sides? It looks like it may be whats holding the black piece on. No tools Ive come across could remove that.
First, what type of screw is it, whats it holding on, and will it help?

Problem. -

1993 Honda Civic EX Coupe
D16Z6
AEM cold air intake (put stock intake back on, no change. Intake was put on more then three months before the problem started.)

First, problem only occurs while idling. never when acclerating, braking, coasting.
only when clutch is pressed in or car is in neutral.

While warming up, it would surge 15-25
then once it was warm would idle 1-2.

with iacv not plugged in, cars base idle is 1.5, with screw completly in.

Though when driving I do experience the car surging when I first touch the accelerater and again when I release, (annoying when your just trying to keep at a certain speed and just need to touch the accel. and then release often), the car seems to surge foward and the back respectivly. This has nothing to do with the idle, and may be something completly differernt but Im adding just for the info.

took off the throttle body cleaned it of carbon.
cleaned the intakes on the iacv.

no change

screwed in the screw at the back of the thermal valve.

when started cold, car would idle around 2, for about a minute. then start
surging about a minute later after it had warmed up at ~1-2 maybe a little higher, but would always settle at 1-2 when warmed completly.

cleaned the idle screw of carbon
replaced the main vacuum lines

*checked the lower port in the intake manifold. There is vacuum.

no change

today opened up the front of the thermal valve and couldnt find anything to change.

This is as much info as I can think of at the moment.
Thanks for the interest.


[Modified by StockYellow, 5:25 AM 3/7/2002]

 

Just to add a little more info on IACV's:

The 2-wire types use a pulsed waveform that opens a plunger (allowing air to pass) against a spring. So, when testing these, if you unplug it, the idle should always fall because the spring is closing the plunger against its seat and not allowing additinional air through. If you unplug it, and the idle does not decrease....you've found a problem.

However, the 3-wire types are a rotary design, and use a (-) and (+) signal to control the posistion of the rotor. This type of design can bypass larger amounts of air than the 2-wire type, thus you won't typically find other fast idle gizmo's on an engine that uses this design. When testing these, you can not simply unplug it and expect the idle to go down, the opposite is actually true, unplugging this control valve will INCREASE the idle, as fixhondas stated earlier.

Like I had said earlier, according the Helms, the procedure to adjust the idle on each is a little different...being that you UN-plug the 2-wire types and leave the 3-wire types plugged in.

Now, of course, tyring to troubleshoot an idle problem without first making sure of the 'other' things is just leading you to shoot yourself in the foot. So, have you checked the following:

Air cleaner (yeah, trivial, but I'll post it anyway)
PCV system
Timing
Valves adjusted correctly...I believe its valves that are to TIGHT will yield an unstable idle.
Exhaust system is not clogged
Good compression, minimal blow-by
TPS set correctly (I believe its <10% with a scantool, or .5V with a meter)
Coolant bled correctly
And generally, just healthy sensor inputs. I once read that a person had an idle problem that was resolved through changing the O2. Now, I didn't think the O2 had an effect on the idle...but I could be wrong..can anyone confirm this?

I'm sure you could add on the list, but if the majority of the 'system' isn't up to snuff, then how can we troubleshoot 'locally'...know what I mean.

And anytime I wash my engine bay, having dis-connected the battery first, I'll have to do an ECU reset...where-in I just start the car and let it idle till the cooling fan comes on, then shut down the car. If I don't do this, just pulling out of the driveway will yield the 'hunting idle syndrome'. This is for a stock 99 Civic hatch CX, D16Y7.


[Modified by EE_Chris, 1:49 PM 3/7/2002]

 

I just fixed a similar problem. Everyones past posts are very helpful, as idle problems can be a combination of things.

If you have confirmed that there is no vacuum leaks, coolant is bled, IACV, FITV, TPS and idle air adjustment screw are ok-- check the throttle stop screw/bracket.

My problem was the throttle stop screw bracket was slightly bent. This allowed too much air through the throttle body at idle. I adjusted the throttle stop screw and it idled perfectly.

Make sure you check/readjust the TPS after any change in the throttle stop screw.

HTH

 

""Now, I didn't think the O2 had an effect on the idle...but I could be wrong..can anyone confirm this?""

EE_Chris... Good info on your post. As for the O2 affecting idle... My '90 Si would vary 50rpm in idle with a slow and lazy O2 sensor. You could actually watch the voltage output change in sync with the idle change. I know it's not the 1k to 2k idle surge being discussed, but in a small way it would seem the O2 sensor can affect the idle.

 

here is my problem in detail...
the car used to run perfectly fine when my friend had it. it all started after he used some fuel injection cleaner to clean the intake manifold and tb. i guess that put too much in and that car has started to get that surging idle since then. when the car first starts up it idles perfectly, but after it starts to warm up a bit (like 5-7 minutes) the idle will start to surge from 1100-1900 rpm and does not stop that. it is only at idle and has not affected performance of the car...just gas mileage.
what i have looked for???
-i have searched the whole car for vacuum leaks w/ carb cleaner and found nothing...i have done this four times. so i pretty confident it is not a vacuum leak.
-i have also tried 3 different iac, all off OBD-I manual transmission cars and they were pulled off cars that did not have idle problems.
-i have tried bypassing the fast idle valve w/ silicone to try and fix it...somebody told me to do this and it might fix it. it seems to have helped it because the car idles normal longer than before, but did not fix it.
-i have tried putting on a new tb w/ a good tps on it (off a manual OBD-I car), but that didn' changed anything
-i replaced my thermostat because the car had a problem w/ heating up...that didn't help and i have bleed the coolant many times to see if that would help...nothing
-i have tried to unplug the iac and cover the whole in the tb to see if the car would die...it doesn't keeps idling the same. and i tried to reset the idle w/ the idle adjustment screw...nothing

there...i think that's everything. any ideas???

 

Stockyellow-

Great info- now, with the throttle closed- what is the voltage at the TPS? (middle wire + and body ground -) we are looking for @ 0.49 volts. Also- you said when the IACV is unplugged the idle stays at 1,500 rpm correct? Plug the bottom port in the throttle body with your finger (IACV unplugged) - does the idle speed drop or die or stay at 1,500 rpm? Also- be sure there is some slack in the throttle cable- too tight= poor idle.





[Modified by fixhondas, 4:27 PM 3/7/2002]

 

Hatchmobile-

Pinch your PCV valve hose- any change?
With the idle screw all the way in and IACV unplugged, what is the idle speed? Plug BOTH ports in the throttle body- what is the idle speed then? Cover the throttle body opening with your hand- does the engine still run? At what speed? What is your TPS voltage at closed throttle? (middle wire+ and body ground-)

 

when i unplug the iac...idle drops to 1500 and there is a little surging +/- 50 rpm
tps at voltage is .15...bad isn't. we might the problem figured out here
when i put my hand over the tb opening...idle does not change

 

i think you may find that it is you throttle position sensor (TPS)...
this may need to be ajdusted to factory specs again. (0.5v at closed throttle)

have you done anything around the TB to affect this sensor?

hth,

t..
_______
posted 8:17 AM 2/28/2002

 

i've pulled off the tb a couple of times...i wondering if that fuel cleaner that my friend used affected it??? i have another tps...i'm going to try and put that on and adjust it so it idles normal and at .5V. thanks for the helps guys