Tuning the idle and IAC counts w/ T-Link

[d0n_3d]

Hooked T-Link up tonight and I was playing around with the idle settings...I set my minimum idle air screw back a little bit than where it was so i could get my tps 4.55+ at WOT

so i set the tps to .42 with the ignition key turned to on but not started...then i went WOT and it was 4.70 so it's all good right? well not really...

once i started the car the IAC counts jumped way the hell up to 90-110 at idle...now i know it's suppoed to be between 10-40 so i am more than double the limit...car seems to idle ok but why are the iac counts so high??? the tps is set correctly??? what gives?

 

[TurboDave]

Originally posted by d0n_3d
Hooked T-Link up tonight and I was playing around with the idle settings...I set my minimum idle air screw back a little bit than where it was so i could get my tps 4.55+ at WOT

so i set the tps to .42 with the ignition key turned to on but not started...then i went WOT and it was 4.70 so it's all good right? well not really...

once i started the car the IAC counts jumped way the hell up to 90-110 at idle...now i know it's suppoed to be between 10-40 so i am more than double the limit...car seems to idle ok but why are the iac counts so high??? the tps is set correctly??? what gives?

They interact with each other which is why it's quite time consuming to get them "right". Patient, and keep at it. My method is to do the IAC first. With yours so far out, I'd recommend adjusting the IAC's down in 10-20 count incraments, then go to the TPS and get it to the proper settings, then back to the IAC and back to the TPS.
I like to shoot for a .42 idle (key on engine off), and >4.60 WOT (key on engine off).

Once you get them where you like them (IAC 15-40) and TPS set you'll have a "smoothy"

 

[d0n_3d]

when adjusting the iac valve...do i turn it in or out to decrease iac counts??? my tps is set perfectly but my iac counts are near 100 at idle...how do i get that thing down? do i just unscrew the iac out? i believe it's all the way in right now but don't quote me on that...i'll have to play around with it today...

 

[dthrock]

Check this

I was just reading this yesterday. Should help you out.

http://www.gnttype.org/techarea/faq/IACresetscan.html

David

 

[LinearX]

My only question is what mode do you put the ECM in while doing this? In the IAC reset instructions from the service manual it says to jump the 2 points on the ALDL connector. Are you supposed to put the ECM into ALDL mode with the scan tool as well, or just leave it normal and adjust?

 

[OKTurbo]

You're not really adjusting the IAC itself. You may want to remove it and clean it....carefully. Check out the procedure on gnttype.org.

When you move the adjustment screw on the throttle linkage bracket you are affecting what range the IAC will work in. The problem with the minimum air adjustment screw is that when you move it....it moves the throttle plate...which also moves your TPS.

So any movement of the screw will change your idle TPS voltage. This is why you have to kind of move back and forth between the screw and the TPS.

Don't get hung up on hitting exactly .42 volts on the TPS. You want it somewhere between .40 and .46. Over .46 and the computer won't think you are at idle anymore and it will run funny.

The computer chip determines the idle speed. Most chips are set to 750-775 rpms at idle. The computer moves the IAC in and out to keep the idle speed at 750rpm. If the load at idle changes....like if your A/C comes on...the IAC will open a little to let the engine compensate for the added load...you can watch the IAC numbers go up on the scantool.

If your IAC numbers at idle in P/N are 15-30 and the TPS is .40-.45 the car should idle fine. If the idle is still funny check your BLM's at idle. The BLM should be around 128 +/- 15....if your BLM is much above 128 it means that the computer is ADDIND fuel....a good indication of a vacuum leak letting extra unmetered air (MAF isn't seeing it). The IAC is a stepper motor that moves a pintle in and out to bypass air around the throttle plate. If the IAC numbers are out of range it won't have good control of the idle speed.

Another thing which can make it idle funny is a EGR valve that isn't closing all the way....usually caused by carbon build up.

Sorry so long, but I hope that helps explain it a bit.

Good Luck,
John

 

[OKTurbo]

LinearX,

There is a procedure for IAC reset where you put the car in ALDL mode. You can find it on gnttype.org. (link posted above) I do this when I remove the IAC for spring cleaning.

I've had good luck just leaving the car in normal mode and adjusting things from there. Just be sure it is warmed up or you'll be chasing things around.

John

 

[LinearX]

Originally posted by OKTurbo
LinearX,

There is a procedure for IAC reset where you put the car in ALDL mode. You can find it on gnttype.org. (link posted above) I do this when I remove the IAC for spring cleaning.

I've had good luck just leaving the car in normal mode and adjusting things from there. Just be sure it is warmed up or you'll be chasing things around.

John

Yeah, the one on gnttype.org (there may be two) is one that came out of the Buick service manual. I was a bit confused on whether or not to put the ECM in ALDL mode or not.

 

[kenmosher]

There are a couple procedures on the site ...

The one linked to here in this thread addresses using a scan tool to set it.

The reason why you short the pins in the "manual" method is to retract the IAC motor completely (so it doesn't do anything during the initial adjustment of the minimum air setting).

• Basically, with the "manual mode", you disable the IAC by shorting the pins and take it out of the equation.
  
  Then you set the mechanical minimum air setting (by tweaking the screw to set the base idle around 550 RPM).
  
  Then you plug the IAC back in and the ECM starts adjusting.

The scantool procedure is much easier and you don't have to mess with all that.


http://www.gnttype.org/techarea/faq/IACresetscan.html

 

[d0n_3d]

hey ken....does it really matter if the WOT tps value is between 4.55 and 4.85 volts? because i couldn't get my tps set at that kind of WOT range without having the IAC counts very high...so i got my iac counts to 20-30 and the tps to .42 and the WOT reading is 4.36...is this acceptable for PE mode? steve wood was saying that as long as the tps at WOT is 75% of 5.00 (above 3.75) then the ECM goes into PE mode...

 

[kenmosher]

I personally like to set the TPS around 4.55, just for insurance purposes. TurboDave had a pretty good post on the List at one time that showed that it's a good idea to have it in that range to make sure you have enough for some of the stuff the custom chip programmers do.

There's no reason you can't set the TPS and then adjust the IAC counts. They interact, so you have to go back and forth a bit, but I like to set the TPS first, check the counts, and you fiddle a bit back and forth until everything is set like you need it.

 

[kenmosher]

I personally like to set the TPS around 4.55, just for insurance purposes. TurboDave had a pretty good post on the List at one time that showed that it's a good idea to have it in that range to make sure you have enough for some of the stuff the custom chip programmers do.

There's no reason you can't set the TPS and then adjust the IAC counts. They interact, so you have to go back and forth a bit, but I like to set the TPS first, check the counts, and you fiddle a bit back and forth until everything is set like you need it.

 

[d0n_3d]

well see the thing is ken...if i adjust the tps and THEN the iac...i have to adjust the iac according to that throttle stop screw correct? well when i turn that screw to lower iac counts the tps is also being changed (forgot higher or lower) so then i readjust the tps again and then keep doing that until the iac counts are 20-30 and then i adjust the tps to .42

but THEN the tps won't go past 4.40 because the throttle stop screw has the throttle blade pushed a little more forward and the tps range is smaller than before...it's like i am forced to either have a good idle and not have the 4.55 tps or i will have a ****ty idle (throttle screw sticking almost all the way out) and have the full range of >4.55

so what gives? or is my IAC just messed up???

 

[OKTurbo]

I'm not Ken....but

One trick that works it to loosen both screws on the tps and push it as far forward as you can and tighten it up. Then loosen the top tps screw just enough so that you can "bump" it to get your idle setting.

What this accomplishes is that you move the tps wiper arm further out on the pin that is connected to the throttle blade shaft. It will give you more movement of your tps over the throttle range...hopefully enough to get the WOT tps voltage where you want it.

This usually works pretty good. Yeah it is a PITA, but the little things count on these cars. You are correct in your thinking and you have a excellent grasp on what you are trying to accomplish....don't give up.

Good Luck,
John

 

[d0n_3d]

well...i was told to do that and i did but when i pull the tps sensor forward it will start to slant to the right and when i tighten it it goes back to my original position...i still can't get the tps higher than 4.40

i will keep workin on it i guess

 

[OKTurbo]

Many guys will say that you don't have to enlarge the slots in the tps....I'm guilty...I did it to mine.

This will give you enough adjustment. I used a dremel tool to "woller" out the slots. An xacto knife works...or a cordless drill.

You may have gotten lucky and have a tps with a smaller range....if you have another one you might try it?????

As you can see, it isn't brain surgery....just a major PITA if things don't go ~by the book~.

(Don't forget that the tps is working against the throttle return spring....if you have an extra hand...let someone hold the throttle open while you push the tps forward and tighten it down...also take a look at the pin and make sure it isn't bent)

You'll get it,
John

 

[dthrock]

Floor mats

Ok, something that I found out the hard way, your floor mats will cause you to not be able to get full range on the pedal. My tps went from 4.4x to 4.9x just by pulling the floor mat out. You probably arent as new at this as I am but sometimes the obvious things get overlooked.

David

Originally posted by d0n_3d
well...i was told to do that and i did but when i pull the tps sensor forward it will start to slant to the right and when i tighten it it goes back to my original position...i still can't get the tps higher than 4.40

i will keep workin on it i guess

 

[d0n_3d]

i know about the floor mat thing...trust me i had mine removed when doing this...i also went WOT by pushing all the way down on the black throttle thingy lol

once my inverter for my laptop finally comes (damn fedex!) i will test all this stuff out again...thanks for the replies