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Discussion Starter #1
Hello all,

I'm running a gen 3 3SGTE and currently in process of tuning it on a Megasquirt ECU. I've found as others have that our stock ECU's must have held the IAC closed when under boost, because when the valve is unpowered it is open.

This could be fixed by running an additional ECU output to the RSC (close valve) pin on the valve, but the simplest method and one which I think would prevent any risk of boost leaks due to the valve not sealing shut totally, would be to run a T piece on one of the joiners in my boost pipes and run the IAC pipe into the boosted side of the intake pipework.


Does anybody know of any problems that could be encountered by doing this?
From reading other threads it seems it has been done before.
I'm interested to know if anybody has seen any problems with failing Idle valves, or strange idle behaviour, or any loss of power, etc. after making this change


Thanks all,
Dan
 

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So you mean, running a small pipe off the intercooler cold side pipe pre throttle body and plumb it into the idle valve? So if the idle valve did 'leak' then really it couldn't as boost pressures would be even across both sides of the valve.

I don't see why it wouldn't work but then that begs the question, why does the OEM run it off the airbox in the case of the GEN3 3SGTE or the intake pipe pre turbo on the GEN2 3SGTE being AFM after the airbox.

How bad are these boost leaks if left the OEM way?
 

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I don't see why it wouldn't work but then that begs the question, why does the OEM run it off the airbox in the case of the GEN3 3SGTE or the intake pipe pre turbo on the GEN2 3SGTE being AFM after the airbox.
You're right on gen2 you have to run it so the AFM sees what air is being drawn in at idle, gen3 is speed density so it doesn't matter what is going on before the throttle body. I ran a check valve on my IAC valve air supply but I don't think it changed anything I would just to it like it originally was. If it were really a problem everyone would be fixing it.
 

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My Aem doesn’t close iacv when boosting. Currently, my iac is vented to atmosphere with filter. That means I have a known boost leak. No issues that I am aware of.

I have considered plumbing it back into the A2W intercooler core that is sitting on top of my motor, but cannot find a reasonable justification to exert that effort.

Previously, it was plumbed pre-throttle plate with a smaller diameter hose than its output is sized. That choked the iacv, preventing it from having enough range to modulate the rpm from 1,000 to 2,000.
 

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I had mine plumbed in like this (T'd into the cold pipe) back in my 3S days. Never gave me any problems, but I think I only ran it that way for maybe a year before parting out that motor and swapping to the v6.
 

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Discussion Starter #6
Thanks for the replies!

So you mean, running a small pipe off the intercooler cold side pipe pre throttle body and plumb it into the idle valve? So if the idle valve did 'leak' then really it couldn't as boost pressures would be even across both sides of the valve.

I don't see why it wouldn't work but then that begs the question, why does the OEM run it off the airbox in the case of the GEN3 3SGTE or the intake pipe pre turbo on the GEN2 3SGTE being AFM after the airbox.

How bad are these boost leaks if left the OEM way?
Yes this is exactly what I mean, I would put a silicone T piece with a 25mm to 16mm reducer in front of the TB and run the IAC to that.
I am not clear on why Toyota have done it the way they have, but Nissan S14 SR20 and RB25DET both have exactly this, pipe from IAC on intake manifold directly to the cold side boost pipe.

I'm not sure how bad the leaks would be, but unplugging the valve is enough to make the idle rise to 2000rpm (on my car, maybe around 1600rpm is the Toyota spec from memory), so this is enough to flow more charge air than I'd like to lose.

You're right on gen2 you have to run it so the AFM sees what air is being drawn in at idle, gen3 is speed density so it doesn't matter what is going on before the throttle body. I ran a check valve on my IAC valve air supply but I don't think it changed anything I would just to it like it originally was. If it were really a problem everyone would be fixing it.
I've never actually seen a stock Gen 3 airbox before now, didn't realise the IAC intake position changed Gen2-3. I am running a Gen3 head on a originally Gen 2 car, currently still use the Gen 2 IAC pipe position just before the turbo inlet.

I think it's not really a problem unless you are using an ECU which has no option to shut the valve depending on boost pressure. Anybody using a Stock ECU or certain Standalones which have that feature won't have an issue (or at least will have a much smaller boost leak) .

Running a check valve would be another option, what kind of valve did you use? No weird noises or problem getting enough air through it for idle control?


My Aem doesn’t close iacv when boosting. Currently, my iac is vented to atmosphere with filter. That means I have a known boost leak. No issues that I am aware of.

I have considered plumbing it back into the A2W intercooler core that is sitting on top of my motor, but cannot find a reasonable justification to exert that effort.

Previously, it was plumbed pre-throttle plate with a smaller diameter hose than its output is sized. That choked the iacv, preventing it from having enough range to modulate the rpm from 1,000 to 2,000.
Does it not keep you awake at night knowing that boost is escaping? Are you running a big turbo with plenty of spare efficiency to make the boost back up to your target level?
Thanks for the tip on diameter, Currently only T pieces I can find have a bigger diameter than the stock pipe and will need a reducer, so shouldn't run into that problem

I had mine plumbed in like this (T'd into the cold pipe) back in my 3S days. Never gave me any problems, but I think I only ran it that way for maybe a year before parting out that motor and swapping to the v6.
OK thanks, good to know somebody has done it without finding a (short term) problem!



Thanks all!
Dan
 
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