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IAC Does not close as RPM increase


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I am trying to setup my IAC and it doesn't close as RPM (or TPS position) increase.  I have a 3SGTE Gen 4 with a stock throttle body and IAC (same wiring as 1ZZ IAC).   I have confirmed that the IAC is properly wired and it seems to adjust properly with duty cycle changes, so its not stuck.   With the IAC open it's a giant vaccum/boost leak.

I noticed that on most posts people set the TPS and RPM lock out at very low values like 400 rpm which is way below normal use.   I've tied to adjust RPM lockout to 1500 RPM and the TPS lockout to 5% but nothing happens with the IAC.  Shouldn't the IAC close (duty cycle 0%) if the RPM or TPS is above the lockout values?

Any help would be great.



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On the 3SGTE Gen 4 (ST215) the valve is to atmosphere.  It has hose that typically routes to the air filter box.   Most people (like me) run a small filter on the IAC port in place of the hose.

I can change the valves in the idle base position table to 0% duty cycle and the valve does close.   Should I just expand the idle base position table to 9000 RPM and add all 0s in higher RPMs?  

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You could try something like below.  In this example the valve would close above 2000RPM.  Minimum clamp would have to be zero, all the offsets like dashpot, PS, fan, AC would have to be zero.  



The other option would be to set the idle output to a CAN aux, then use that CAN aux to control a GP PWM, you could then just turn off the aux above a certain RPM or TP or whatever and still have a normal base position table with all the offsets working.

Having said that it wont be nice to tune around the point the valve opens and closes and the factory would have had to put in a lot of work and some odd strategies to get a smooth transition through that operating range.  It would give a better result if you plumbed it back into the intake pipework.    

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  • 2 weeks later...

I typically set the table like above versus MAP instead of RPM and set it to close above 105kpa (setting base position row values at 100 and 105kpa).  I don't care too much if the IAC hangs open off boost as long as the air source is filtered.  If you're getting a huge vacuum leak - is it causing the car to hang above idle speed?  Is it just the noise you are having issue with?

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