IAC Restrictor Woes

FalconGuy016

New Member
Oct 26, 2004
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Northern VA
This is for anybody who has done a IAC restrictor mod to fix those annoying GT revs.

Ever since day one for me I have never gotten it really *right*. My copper cap is probably a tab bit too restrictive at the moment, but that probably doesn't relate to the problem. To my experience so far the effects of the cap affect the idle, between shifts, and engine braking (every instance where my foot's off the gas). The only area of benefit seems to be between shifts, which is the whole point of the mod, and is something I really can't live without anymore.

Which sucks because the low startup idle is painful in the cold weather and the engine braking is much more jolty (feels like the same drivetrain slack you would normally feel but worsened). I have grown a habit to never entirely let off the gas to engine brake, rather just ease it in, and to add gas on a cold startup to the regular 1100-1200 warm up RPM period.

All of these downsides are fine by me if I can have my quick shifts, but another thought keeps nagging on me now. Does this IAC mod cause me to run richer? I notice when I first start up and rev a little the car sounds really badass, almost gurgly as the revs come up and down superfast. But after a few minutes of driving the tone softens and the revs slow a lot more, as if the computer were adapting to something. Something such as an abnormal restriction of airflow, and remedying that by adding more gas. I still get slightly faster shifts but the effect is clearly changed. I don't want to be running needlessly rich all the time if that is indeed the case.

Does this sound right to anybody else? I almost can't live without this mod, but I won't run it if it will be doing so much more negative than positive.
 
white-04 said:
Did you buy it from the guy who was selling them or did you make it yourself? Maybe making the restrictor hole slightly larger would help things out...

Nah I built my own plate that was a superb piece of machining :D but I found the cap just as effective and much more user friendly for tuning. I am gonna try a larger hole but it's already as big as I think I can go. What I really wanna know is if this affects the fuel mixture.

And 1LowGT, really? I'll go try that now and see if I get the same thing. Although I really doubt it, the revs fall ridiculously fast, but I'll go see.
 
Ive bought a plate and used the copper plug. Low idle when cold and Ive noticed till Ive driven around for quite a while when I get to a stoplight it will idle at 1000-1200 RPM. It stays there for about a minute and then drops, I have to blip the throttle to keep it from stalling, then will idle at normal RPM. Ive even tried playing with idle speed using Predator. I dunno, I like how it cruises so I'll not mess with it for now.
 
You have to remember restricting the IAC valve inhibits the functionality of it, so getting it right is hit or miss. If you really want to speed up the rpm drop the correct way to do it is in the tune. I noticed to have an xcal 2. I don't know what params you have available, but look for a dashpot settings. Adjust the dashpot delay, and dashpot mph clip until you get the rpm drop you want. If you don't have these params available, you may have to have your tuner do it.