Let's try to make this an informative thread that people can come to if they have questions about the IACV.

I'll start with my problem and understanding and hopefully we can go from there:

itr motor, cams, itb's, header, etc; I currently have the plug to the iacv connected. BUT I don't have the iacv connected to my itb's nor to my vacuum canister.

Now I have a plate that bolts to the iacv and has a spot for a vacuum line to theoretically go to the itb's or vacuum can, and the other port is for a filter for ambient air. The coolant ports on the iacv I have capped off - as I don't run coolant from the head to the plenum (obviously).

But doesn't the iacv normally allow additional air into the motor when the throttle plate is closed? Like when the ELD tells it to in order to keep rpm's up say on coastdown to a stoplight when you are off the throttle?

Why shouldn't I just disable the iacv in my ems (crome)?

Is there something about the iacv that could prove advantageous to me?

 

As the name implies.. the IACV is used by the ECU to allow a certain amount of air into the intake, depending on accesory loads and other conditions, to achieve a desired idle RPM under varying conditions. The absolute base idle is set with the air bypass screw in the throttle body, but that is a fixed amount of air. The IACV adds more air as needed. It is advantageous to have.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Perfectionist &raquo;</TD></TR><TR><TD CLASS="quote">As the name implies.. the IACV is used by the ECU to allow a certain amount of air into the intake, depending on accesory loads and other conditions, to achieve a desired idle RPM under varying conditions. The absolute base idle is set with the air bypass screw in the throttle body, but that is a fixed amount of air. The IACV adds more air as needed. It is advantageous to have.</TD></TR></TABLE>


Well, in order for it to do me any good I'd have to run it to four lines which go to my plenum after the individual throttle plates.

I don't know what it'd do if I ran it to my vacuum can..... guess I can datalog and see. LOL

 

Here's how I think it's SUPPOSED to work in a stock engine. ITBs are a whole different thing, & I'm not completely sure of the best way to use your IACV.

It's job is to add air to stabilize idle speed while engine loads are changing. The ECU controls the IACV based on rpm, forming a closed feedback loop. In order to keep it in the linear portion of it's range, the IACV isn't supposed to ever really CLOSE. Your base idle adjustment is set so the IACV needs to be open some even when there's no extra loads.

In addition, the ECU will order the IACV to open a bit to anticipate any loads it knows about. For example...
- AC clutch engages
- PS fluid pressure is high (indicating higher PS pump load)
- ELD indicates high electrical load
- radiator fan switches on (which isn't measured by ELD for some years/models)

On newer engines (maybe starting about '98?) the IACV also incorporated the function of the FITV. So now it's job includes fast-idle when the engine's cold.

I think you want tubes from the IACV to all your ITBs, but make them small enough so the ITBs can't really comunnicate with each other too much. You don't want to make your IACV plumbing into another inlet plenum.

 

No. Sounds like you have a good grasp of what it is for. The only thing I can think of is a cold start situation.

Just get used to the idle moving when the alt kicks in, or the fan comes on. We are talking about 50 rpm's so it is not that much to worry about.

 

the iacv is there to make life easier on us; i dont see why to disable it.
I run it to a vaccum box and then to each individual throttle body.

It helps a lot on stalling with itbs and light flywheels, you dont have to adjust idle because of temperature changes and such.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">Let's try to make this an informative thread that people can come to if they have questions about the IACV.
Is there something about the iacv that could prove advantageous to me? </TD></TR></TABLE>

Only if you're prone to sitting at a light w/ the lights + climate control on + stereo blasting. It's also useful when fan kicks in, or if ou for some reason use power steering without applying throttle (some people like to row the wheel around when stopped, which is stupid).

You can hard lock it to a slightly higher idle RPM and additional load will cause it to drop, but as long as it doesn't drop below stall it will be fine.

If you haven't had any stalling issues by now and your idle is not obnoxiously high - just leave it as is.

 

actually, my idle is set at 800rpm in crome but for some reason it sits betwen 1200-1500 no matter the ELD or temperature.

except for when i turn the ac on - then it sits at 800. *shrug*

I'd have thought the iacv could only raise the idle by letting more air in. How could it take air out of the plenum?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">actually, my idle is set at 800rpm in crome but for some reason it sits betwen 1200-1500 no matter the ELD or temperature.

except for when i turn the ac on - then it sits at 800. *shrug*

I'd have thought the iacv could only raise the idle by letting more air in. How could it take air out of the plenum? </TD></TR></TABLE>

are you getting a high/ jumping idle with the iacv hooked up?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">I'd have thought the iacv could only raise the idle by letting more air in. How could it take air out of the plenum? </TD></TR></TABLE>Actually the system seems to be designed/programmed to operate with the IACV always open at least a little. That's why you set base idle (IACV unplugged) at lower RPM than normal operating idle. For example 450 RPM for my '95 GSR.

If you set base idle too high, then your operating idle gets unstable whenever the IACV tries to go completely closed. It's not good practice to design a control system to use it's control element all the way to the end of it's range.

 

how does it allow air in if it is the back of the IM

 

my itb set up ran mint with out them , cold cold starts would be a bit trickyer lol

i tihn the whole iacv is way over thought .

heres my very basic take on it .

take the throttle stop out ot the TB and the iacv should still work .although my car wouldnt run right with the iac not conected even though it wouldnt trow a code (weird)

all it is is a controled bypass for your idle air.

when people bring me there cars with the up and down idle . if cleanign and all that doenst help then all it tals is to close or open th etrhottle stop a tad , if the throttle is open to much the iac tends to try to close its self up since the idle is where it should be , but the iacv cant close enough , then it opens and begins the up and down cycle .

when its really cold out . iac acts like a choke .
and i guess its as simple as that .

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MidwestAutoWorks &raquo;</TD></TR><TR><TD CLASS="quote">how does it allow air in if it is the back of the IM</TD></TR></TABLE>Air comes in to the IACV thru a small port in the bore of the throttlebody, just upstream of the throttle plate. That little hole is connected to a small passageway over to the IACV. From the IACV there's another small passageway into the plenum of the IM.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">How could it take air out of the plenum? </TD></TR></TABLE>

It doesn't. It can only add to it, which is why it's important to have the base idle speed set correctly.

 

Your vacuum canister is already hooked into all 4 runners correct?
If so just add the IACV to the vacuum canister, with the tubes hooked to each runner the vac canister's pressure will be near exactly like a plenum's would be, with the exception of the idle screw on a throttle body setup.