legacycentral bbs

So before I start I know a lot here are going to be all tweaked over some reason or another... And here are my reasons for doing this.

1) I discovered that the ej20g IAC valve and top thingy (motor?) are different from the Legacy Turbo one. Yes, one could possibly swap it to the Legacy Turbo one, but I've always had problems with the motors going bad... So I decided against that.

2) The 20gs IAC Valves motor basically went out and wouldnt adjust at all (it was stuck at 3500 rpm ish) and I didnt want to reuse my ej22t one.



Basically what I have done is bypassed the stock engines Idle Air Control. I got the idea from how Andy and Daves car works with the standalone. And they run by adjusting the idle screw, and work just fine, no they dont like to run totally smoothly until warmed up, no the car wont appreciate really cold weather, but I basically got sick of dealing with the constant headaches of swapping the IAC motors.

I figured that the IAC doesnt play an important role in fuel management at idle because the ecu is controlling fuel based off of the MAF and o2 sensor readings. Fuel Trims are unchanged since removing the IAC.

I realized the IAC valve is basically a 2nd throttle body like entity that is electonically controlled by the ECU, so why not trick the ECU into thinking it has control and just manually adjust the idle one the throttle body? Thats what I did.

What I did was...

(With the car fully warmed up so you can acurately adjust the idle)

1) Adjust the idle screw up 3/4 of a turn.

2) Remove the IAC motor (two screws on top of the IAC) However leave the IAC motor plugged in but move it to an inconspicuous place where nothing will happen to it. This makes the ECU not throw a code and think it still has control.

3) Close the Valve turn it all the way to the left and this will close the valve, what I did as a temporary thing to make sure this would work was put a dab of super glue on it to hold it shut before I removed everything.

4) Start the car, its best to have the car fully warmed up, that way you know what the idle will be at fully warmed up, instead of cold start.

5) Adjust the idle using the idle screw to the desired rpms.

Words of Caution...

Doing this makes cold start idles rough, mine idles at about 6-700 rpm when cold. However by the time I get to the end of my street it starts to idle better, by a 1/4 mile from my house its all normal and idles at 900 rpm like it should.

Doing this also makes the car very prone to a horrible idle if there are any vacuum leaks. Why? Because the car cant adjust the IAC to compensate.

And I dont know how this will do in very cold weather, I'm sure it will start like shit in very cold weather, just like a car with a standalone without IAC.

With all that said... I actually really like not having the IAC, because of all the troubles I've had with it, and it idles phenomenally when warmed up, and there arent any more probs at all, the only cost being a little rough cold start (not that the car doesnt want to start, it just idles low).

So yea, just wanted to share the little mod to fix my ever persistent IAC woes

frees up engine bay a bit to, making it easier to work on.
i like it

nice spence

You've essentially given your engine an extremely narrow window in which it will idle. You will have issues, especially in the winter and with any elevation changes.

But hey....it's your car I'd just caution others on doing this...

Legacy777 wrote:You've essentially given your engine an extremely narrow window in which it will idle. You will have issues, especially in the winter and with any elevation changes.

But hey....it's your car I'd just caution others on doing this...

Hmm. interesting.

Well I'll have to see what the long term effects will end up being, because I've only had the car running this way for about a week.

My suggestion would be to run two new dedicated wires from the ECU pins to the IAC valve motor. That will eliminate any wiring issues. From there, I'd get a good motor and swap it over.

Yeah, you'll spend less money and have less headaches if you just address the issue properly. Do what Josh suggested and go from there.

That's not to say that your idea isn't creative and won't work, because obviously it does! But as Josh said, you'll run into problems in different weather conditions and altitudes.

Thing is, the legacy turbo stuff is different than the 20g stuff.

Idk. If it ends up being a bad thing I'll do that. But I want to give this a try since I'll eventually be going standalone anyways and they run it the way I have mine right now.

smh0101 wrote:Thing is, the legacy turbo stuff is different than the 20g stuff.

Not significantly...

I put a 20g in a 92 SS once and the IAC worked totally fine off the 2.2 ecu

My IAC is not being used because the Autronic ECU model I am using is controling boost, not IAC, can't do both. My car idles perfectly. Starting is harder when cold, especially in the winter, not so bad right now. I installed a Subaru engine block heater, about $27. Plug it in for a few hours and the car fires right up. For my particular situation, circumstances, lifestyle, etc., it is staisfactory for me. On the ej20k mainfold I will be using, I actually cut off a part of the IAC mounting foundation and have blanked off the hole where the valve goes.

smh0101 wrote:Thing is, the legacy turbo stuff is different than the 20g stuff.

Idk. If it ends up being a bad thing I'll do that. But I want to give this a try since I'll eventually be going standalone anyways and they run it the way I have mine right now.

Is the top electrical piece different? I don't see why you couldn't swap that over.

As for the standalone....depends on what standalone you go with.

I just wanted to dig this up and say that the IAC on my car hasn't had coolant lines hooked up to it for several years now which is effectively how the sensor knows what temp the motor is and therefore how to make it idle. It runs great in freezing weather and hot weather, no big deal.

im alittle curious about the 20g iac on a turbo legacy ecu. is the 20h iac the same as the 20g? im using the 20h iac on my car and am having no problems but want to know of issues in detail.

My car runs with an EJ22T ECU and has an EJ20G intake manifold and IACV.

impreza_GC8 wrote:I just wanted to dig this up and say that the IAC on my car hasn't had coolant lines hooked up to it for several years now which is effectively how the sensor knows what temp the motor is and therefore how to make it idle. It runs great in freezing weather and hot weather, no big deal.

Not to start an argument or anything but the coolant lines running through the IAC and TB are there to help with throttle plate icing, and since the IAC is controled by the ECU and the ECU gets the engine coolant temp from the temp sensor I think thats more why you or anyone else (including myself) don't have problems with disconnecting the coolant lines from the IAC/TB