Blocking IAC on LT1 and re tune

LS1Racer · 12-29-2023, 06:18 PM

I have blocked the IAC ports in my LT1 throttle body and was wondering the easiest way to get the idle air back through to get the right idle. I was going to adjust the blades out with the adjustment screws and reset the TPS in the ECU to zero. Is this the best way to do it or is their a better way to accomplish this? I am running a FAST XFI 2.0 ECU. Also is their any adjustment to the fuel map necessary in that lower end of the map? I am running AlphaN and sequential mode. Thanks in advance for the help.

Jeff Niceswanger · 12-29-2023, 07:07 PM

If you have gotten used to a motor with a properly operating IAC, they have a tendency to spoil you. They will maintain and KEEP that idle at setpoint. Not very keen on Fast. You didn't mention if your dealing with a Superstocker or Stocker. Without the IAC the idles are a bit more contrary on the SS camshafts with their low vaacum, but very tunable. Yes, you will need to run the blades open and reset the TPS, especially with the Alpha.The issue you could possibly have is after getting it happy... so it will idle when cold and going into gear nicely (depending on the convertor)..., as it warms up the neutral idle will go higher than most people like. I build advanced tables so timing will be pulled out and or put in to maintain the desired RPM. The Holley has what they call "Idle Spark" to achieve this, but it only will move it 8 degrees one way or the other. I like 14 to do so,and it takes an advanced table. (If this is on a Stocker, you should not have any issues). Maybe someone with Fast knowledge will jump in here and help.

LS1Racer · 12-29-2023, 07:25 PM

Jeff thanks for the info. Sorry, I forgot to mention it is a Stocker.There is a timing trim table for idle which allows up to 12 degrees adjustment related to target RPM vs Actual RPM. I can adjust with that I believe for temp variations.

Jeff Niceswanger · 12-29-2023, 10:02 PM

Quote:

Originally Posted by LS1Racer

Jeff thanks for the info. Sorry, I forgot to mention it is a Stocker.There is a timing trim table for idle which allows up to 12 degrees adjustment related to target RPM vs Actual RPM. I can adjust with that I believe for temp variations.

You should be good. Set your base idol at 20- 22 and let the trim do its thing.

countrypuppy4865 · 12-29-2023, 10:36 PM

You may also have to adjust numbers on the fuel map at idle. Generally adjusting the screw and/or the fuel map at idle you should be able to achieve idle.

mike britt · 12-29-2023, 10:39 PM

I built an adjustable air bleed to screw in where the IAC goes so I could leave the throttle blade closed at idle.

Larry Hill · 12-30-2023, 08:08 AM

Might want to check with tech if the IAC adjuster replacement is below the throttle blades. The replacement could be viewed as an adjustable vacuum leak. Sometimes tech thinks a little differently than the racer.

Mark Yacavone · 12-30-2023, 01:55 PM

Quote:

Originally Posted by Larry Hill

Might want to check with tech if the IAC adjuster replacement is below the throttle blades. The replacement could be viewed as an adjustable vacuum leak. Sometimes tech thinks a little differently than the racer.

I got bounced at Englishtown, in the early days of EFI for this sort of thing. The car builder was using an auxiliary petc o ck bleeder to control the idle. The IAC was disconnected and dead closed.
Lang and co. had to call CA. for a ruling. They were told that the idle vacuum air had to be controlled by the computer, or not at all. It was okayed in Div 2 ,at that time.

My Escort has an idle screw added instead of the stop screw on the throttle blades.
(IAC disconnected) It works fine with the mild camshaft.

SSGN · 12-30-2023, 08:19 PM

Just curious to why you remove the AIC and the benefits of this? I have Turbo Buicks and still use them with no ill effects. I know our cams are tiny in comparison to a stocker.
Thank for this post,very interesting.

LS1Racer · 12-31-2023, 01:37 PM

I can only speak for my case so take this for what it is worth. My idle would race sometimes and was extremely wonky. I probably could have tuned it better but have read here many times from respected racers to just unplug it or block it. I chose just to block it. I do have another TB that still has an IAC on it if I decide to go back to it.

12-29-2023, 06:18 PM	#1
LS1Racer Junior Member Join Date: Feb 2006 Location: Westminster, CO Posts: 51 Likes: 4 Liked 5 Times in 5 Posts	Blocking IAC on LT1 and re tune I have blocked the IAC ports in my LT1 throttle body and was wondering the easiest way to get the idle air back through to get the right idle. I was going to adjust the blades out with the adjustment screws and reset the TPS in the ECU to zero. Is this the best way to do it or is their a better way to accomplish this? I am running a FAST XFI 2.0 ECU. Also is their any adjustment to the fuel map necessary in that lower end of the map? I am running AlphaN and sequential mode. Thanks in advance for the help.

12-29-2023, 07:07 PM	#2
Jeff Niceswanger Senior Member Join Date: Jul 2003 Posts: 771 Likes: 588 Liked 839 Times in 293 Posts	Re: Blocking IAC on LT1 and re tune If you have gotten used to a motor with a properly operating IAC, they have a tendency to spoil you. They will maintain and KEEP that idle at setpoint. Not very keen on Fast. You didn't mention if your dealing with a Superstocker or Stocker. Without the IAC the idles are a bit more contrary on the SS camshafts with their low vaacum, but very tunable. Yes, you will need to run the blades open and reset the TPS, especially with the Alpha.The issue you could possibly have is after getting it happy... so it will idle when cold and going into gear nicely (depending on the convertor)..., as it warms up the neutral idle will go higher than most people like. I build advanced tables so timing will be pulled out and or put in to maintain the desired RPM. The Holley has what they call "Idle Spark" to achieve this, but it only will move it 8 degrees one way or the other. I like 14 to do so,and it takes an advanced table. (If this is on a Stocker, you should not have any issues). Maybe someone with Fast knowledge will jump in here and help. __________________ Jeff Niceswanger 3740 SS Last edited by Jeff Niceswanger; 12-29-2023 at 07:24 PM.

12-29-2023, 07:25 PM	#3
LS1Racer Junior Member Join Date: Feb 2006 Location: Westminster, CO Posts: 51 Likes: 4 Liked 5 Times in 5 Posts	Re: Blocking IAC on LT1 and re tune Jeff thanks for the info. Sorry, I forgot to mention it is a Stocker.There is a timing trim table for idle which allows up to 12 degrees adjustment related to target RPM vs Actual RPM. I can adjust with that I believe for temp variations. Last edited by LS1Racer; 12-29-2023 at 07:48 PM.

12-29-2023, 10:36 PM	#5
countrypuppy4865 Senior Member Join Date: Nov 2003 Location: Donaldsonville, LA Posts: 966 Likes: 8 Liked 183 Times in 62 Posts	Re: Blocking IAC on LT1 and re tune You may also have to adjust numbers on the fuel map at idle. Generally adjusting the screw and/or the fuel map at idle you should be able to achieve idle. __________________ Jimmy "Cooter" Hidalgo, Jr. 4865 E/SA '04 GTO 4865 SS/GA '99 Firebird

12-29-2023, 10:39 PM	#6
mike britt Member Join Date: Mar 2013 Location: Italy, Texas Posts: 141 Likes: 203 Liked 43 Times in 19 Posts	Re: Blocking IAC on LT1 and re tune I built an adjustable air bleed to screw in where the IAC goes so I could leave the throttle blade closed at idle.

12-30-2023, 08:08 AM	#7
Larry Hill Live Reporter Join Date: Oct 2004 Location: Hickory, Ky Posts: 10,284 Likes: 1,637 Liked 9,458 Times in 1,958 Posts	Re: Blocking IAC on LT1 and re tune Might want to check with tech if the IAC adjuster replacement is below the throttle blades. The replacement could be viewed as an adjustable vacuum leak. Sometimes tech thinks a little differently than the racer. __________________ IHM Used Parts https://ihmusedparts.com 888-821-1817

12-30-2023, 08:19 PM	#9
SSGN Senior Member Join Date: Feb 2006 Posts: 625 Likes: 110 Liked 130 Times in 46 Posts	Re: Blocking IAC on LT1 and re tune Just curious to why you remove the AIC and the benefits of this? I have Turbo Buicks and still use them with no ill effects. I know our cams are tiny in comparison to a stocker. Thank for this post,very interesting. __________________ The more people I meet the more I like my dog Kevin

12-31-2023, 01:37 PM	#10
LS1Racer Junior Member Join Date: Feb 2006 Location: Westminster, CO Posts: 51 Likes: 4 Liked 5 Times in 5 Posts	Re: Blocking IAC on LT1 and re tune I can only speak for my case so take this for what it is worth. My idle would race sometimes and was extremely wonky. I probably could have tuned it better but have read here many times from respected racers to just unplug it or block it. I chose just to block it. I do have another TB that still has an IAC on it if I decide to go back to it.