Setting Idle/checking Iac?????

[PaulRV6]

I am having trouble adjusting my idle per the TB's.COM instructions, my questions are:
What does grounding the ALDL connection do prior to removing IAC connector w/key on? does it make IAC go fully closed?

Why does one procedure say to adjust screw to 500rpm and the other say adjust to 750rpm?

Is there a way to verify if the IAC is working electrically?

What if I cannot adjust the idle speed down to even 750 rpm? Does this indicate the IAC is still too far open? Do I have a large vacuum leak downstream of the throttle plate? Is one more likely than the other or could there be other reasons?

Thanks for all the help!

paul

 

[PaulRV6]

TUNING EXPERTS, where are you?

Ah, where are all the responses when you want them?

Comon guys, need the help.

paul

 

[Ormand]

Idle Speed

The idle speed is controlled by the chip- you can't set it to an arbitrary value. Maybe one procedure is for stock chip, one is for anothe chip? The service manual has 500 rpm, plus/minus 50 rpm, so that would seem to be "stock". I think Thrashers are higher, but don't remember exactly. Better to set the counts in the right range, and let the rpm go where the chip wants it to be.

 

[PaulRV6]

Thanks Ormand, I know that the idle speed is controlled by the chip, but there are instructions in the GNTTYPE.ORG for resetting IAC (improve idle).
Why ground the ALDL terminal? Does this reset the IAC to a certain position? How can I tell if it is resetting to that position, cause I am thinking that might be the problem

Please see other questions on my first post.

paul

 

[OKTurbo]

Grounding the pins on the ALDL puts the IAC in it's "home" position....which I assume to be full open...the pintle all the way in on the stepper motor.

Like Ormand said, the chip controls the idle speed as long as you have the IAC set within it's window of adjustment. The procedure that tells you to set the idle RPM's to 500 also says to unplug the IAC connector. With the IAC out of the picture you adjust the screw on the throttle arm to get 500 RPM's. Then with the IAC plugged back in you ~should~ get IAC numbers around 15-25...

If you have a scan tool you don't really need to go thru the whole routine of grounding the ALDL pins and unplugging the IAC. It's probably a good idea to go ahead and "park" the IAC by grounding the ALDL if you want to actually remove the IAC for cleaning.

Most street chips set the idle to around 750-800 RPM's. The computer adjusts the IAC motor to maintain this set speed.

The most important thing to pay attention to is that each time you adjust the screw to get your IAC number you also will be changing the TPS setting at idle since the TPS is attached to the same throttle plate. If the TPS voltage goes above .46 the computer will think you're not at idle anymore and the RPM's may go up.

So each time you make an adjustment you need to look at both the IAC and the TPS. After each time you tweak the TPS or the screw you'll need to reset the computer by unplugging the orange connector by the battery.

Sorry so long....hope it helps,
John

 

[TR Custom Parts]

This link might help you out! I used TurboDave's method and it worked fine.
http://www.geocities.com/rad87gn/tech/IACTPS.html

 

[PaulRV6]

So after doing this (trying to set idle at 750 per Dave's method) I cannot get that low then I must have a vac leak? Thus allowing more air in or could the IAC be not working? Everything has been cleaned prior to putting this thing back together.
Need your help. Thanks

paul

 

[OKTurbo]

Paul,

What are your IAC and TPS numbers at idle? Make sure the motor is fully warmed up and the computer is in closed loop.

You might ask your chip guy (Gary Mitchell?) to see what he set the idle RPM to.

How high is the idle RPM?

Are you using a Scanmaster or some other scan tool?

A bad vacuum leak will show up as a high BLM/INT at idle. (BLM numbers in the 140-150 range)

John

 

[PaulRV6]

OKTurbo, unfortunately I do not have a scan tool (waiting for new TL), so I am following procedure in GNTTYPE without scantool.
Chip is set at 850 rpm to idle.
With the IAC disconnected I cannot get below 900-1000 rpm with the min air adjustment screw out all the way (throttle stop not touching).

My idle is not very good, it sort of hunts around. That is why I thought I needed to adjust the IAC. With the IAC hooked up it idles down ok but just not stable.

paul

 

[OKTurbo]

Well Paul, I hate to say this, but without a scan tool you're hunting in the dark.

With a voltmeter you can probe the wires going to the TPS and take a look at what you have there. Not so lucky on the IAC numbers though, since they only come thru the ALDL port.

I suspect that your idle TPS voltage is too high...could be a vacuum leak, but you'll need to know the idle BLM numbers to know for sure. Don't forget the basics.....good plugs gapped properly....good plug wires....strong battery....fuel filter...etc. etc.

There is a freeware program called WinALDL that you can use if you already have a notebook PC. You'll have to go to radio shack to get some parts for the interface cable. It's not specific to Turbo Buicks like TurboLink, but it will give you the info you need to track down the problem.

http://www.winaldl.webhop.net/

I use a Scanmaster hooked up all the time, and use TurboLink when I'm at the track. Both are very good tools. A scan tool is a must if you work on your car.

Good Luck,
John

PS....the stock tachometer is not very accurate...if you're reading from it.

 

[Danster]

PaulRV6, just went through this about a week ago and I too got caught up with trying to adjust the RPM's. You CANNOT adjust the RPM's! The chip controls the RPM's during Open Loop and also in Closed Loop with the assistance of other sensors.

Just make sure the IAC and TPS are set correctly. I used the counts for setting the IAC. This did help out in smoothing some of the rough idle. I may have injector issues that may be impacting a total smooth idle. However, I couldn't have done it without my Scanmaster2.

Damn, I'm actually starting to learn something(s). Thanks TB.com!


Dannyo

 

[PaulRV6]

OKTurbo, I did build the WINALDL cable and have used it once but just getting started. So I gusee I can look at IAC counts (if it is accurate) for the info.
And I am not trying to adjust idle speed, only set the TPS / IAC min air setting (to Danster).

I hear ya about checking the basics but everything is new, fresh rebuild with all new parts (except IAC).

I am also using my VDO tach which seems to be very accurate. I will check what WINALDL gives me for IAC counts.

Thanks for the help.

paul

 

[terryk]

I got an email from Jonas Bylund regarding the two errors in the 7148 configuration. MAT is backwards. Try heating the MAT. The temps drop. Retard isn't converted by the 45/255 formula.

He's got other pressing issues and won't be correcting these problems anytime soon. Too bad. Those are two critical data fields. You can do the conversion manually from the raw data.

The other fields appear to be correct so far.

Terry