using ford iac on a buick with fast

norbs

Classic fast, XFI, SPortsman & MS3 programming
Joined
May 25, 2001
I have been running into some very odd iac problems with my car. i have tried 3 different iac's and had the fast box checked, with no problems found. Set the fast to 900 rpm warm idle. Drive the car and the idle is 1200,after 10 min driving. Shut off the car and restart its 900 rpm where its supposed to be. I have played with the idle screw on the tb , and watched the iac counts to make sure its not too far out of range from being open and closed. Maybe my iac housing is worn and the plunger is getting hung up. The ford iac system uses a injector type pwm output, which i heard gives real good stable idle control. Anyway to use the ford iac on a fast system?



Also when cold the idle sometimes sits at 800 rpm and stalls, even though i have it set for 1350 rpm, other times it will come up to the set rpm. A very intermittent problem, which is frustratiing
 
They sell an adapter to put a GM IAC on the Fords when using FAST systems so I seriously doubt there is an easy way to make it work.
 
Originally posted by norbs
I have been running into some very odd iac problems with my car. i have tried 3 different iac's and had the fast box checked, with no problems found.

Try swapping the grn/blk, with the grn/wht leads at the IAC.
They can operate an inverted mode. Swapping two leads reverses it's operation.

I don't know the FAST system, but I've seen this inverted behavior on a stock car.
 
If its going to help, its worth a try. Thanks
 
Right off the bat, a Ford IAC motor will not work. The GM units are stepper motors, and the Ford units are PWM controlled. The hardware to run one vs. the other is totally different.

Has this ever worked properly for you? I am with Bruce on this one. You can wire one of these things to work perfectly, or kinda right sometimes, or not at all. Gee, how flexible... :D

Is this a screw-in IAC motor like a Buick or one of the newer types?
 
I need to know the exact pinouts on the ecm connector for the iac, and how these correspond to the felpro pins. Maybe the harness adapter is mixed up. This is a stock buick gn iac set up. But ever since i installed the felpro , now that i think back it never worked 100% correct.
 
FAST connector:

P2 = IAC A HI (pin A on IAC)
P1 = IAC A LO (pin B on IAC)

R2 = IAC B HI (pin C on IAC)
R1 = IAC B LO (pin D on IAC)

Hope this helps.
 
Thanks craig i just checked it, its fine on that side. ON the IAC side i have

A=blue/white stripe


B=blue/black stripe


C=Green/white stripe


D= Green/black stripe


Is that correct?
 
Those aren't my wire colors so I couldn't tell you. I would go by pin locations rather than wire color as chasing wire colors assumes things that can bite you later. If you check to see that P2 goes to A, P1 goes to B, R2 goes to C, and R1 goes to D, that will verify that the wiring is correct. If so we move on to next possible issue, whatever that may be.
 
My wiring is fine, but I too have a similar issue. I can drive the car fine for awhile, sometimes days, but once in a while the idle will start to creep up. If I rev it, the idle will go higher. If I shut it off and re start it, its fine. I've had it go as high as 1500 rpm. I normally idle around 900-950. Some people have said a vacuum leak could do this, but why wouldn't it show up after a restart? Weird.
 
Originally posted by turbosam6
My wiring is fine, but I too have a similar issue. I can drive the car fine for awhile, sometimes days, but once in a while the idle will start to creep up. If I rev it, the idle will go higher. If I shut it off and re start it, its fine. I've had it go as high as 1500 rpm. I normally idle around 900-950. Some people have said a vacuum leak could do this, but why wouldn't it show up after a restart? Weird.

Sounds like a problem with the IAC reset.
Is the IAC and it's passageway clean?.
 
Typically in GMese, you'll see.

Lt.Blu/Wht *A* Hi
Lt.Blu/Blk *A* Lo
Lt.Grn/Wht *B* Hi
Lt.Grn/Blk *B* Lo

The way to change the motor's direction is just swapping two of the Grn OR two of the blues.

Swapping all four, around gets you no change.

In the full extension mode of the IAC, it should be about .96" from the back of the pintle to the IAC mounting flange.
 
Yeah, the iac is new and the passageway is clean. Did this with 2 different iac's and 2 different throttle bodies, although I suppose the iac housing does transfer from one to the other, so that would have no bearing on this problem. Stupid cars.
 
Originally posted by TS6
Yeah, the iac is new and the passageway is clean. Did this with 2 different iac's and 2 different throttle bodies, although I suppose the iac housing does transfer from one to the other, so that would have no bearing on this problem. Stupid cars.

Does the FAST allow for a forced reset?.
If you have an extra throttle body, then screw a IAC into it, and cycle the key on and off to see if it looks at all right in there.

Maybe one of the FAST guys can say what the IAC reset is, if any, and tell ya what it looks like it does at key off.

There are several GM strategies.
But,
At key off or at key on Iin GM world), the IAC should fully extent, and then count back from the seated posistion to a park position.
 
When you turn off the key with the FAST system, it will extend the IAC as far as possible. It basically just tries to shove it out for some number of counts that is more than enough in any circumstance for insurance. On power up the current position of the IAC is assumed to be zero.
 
Well since the idle goes back to normal, after restarting, it would mean the IAC did reset and opened to a different position than before. Any issues with iac drivers found in the fast boxes? that maybe were changed in new boxes, mine is one of the first few.
 
Originally posted by Craig Smith
When you turn off the key with the FAST system, it will extend the IAC as far as possible. It basically just tries to shove it out for some number of counts that is more than enough in any circumstance for insurance. On power up the current position of the IAC is assumed to be zero.

Unless it goes over 255 on the count, and by some margin, then it won't always fully extend it under all circumstances.

If you measure the counts per inch, and possible amount of travel, you'll see what I mean.

In pestering some parts guys today, I also found some IACs are being shipped fully retracked, instead of extended like GM does.
 
Also while browsing around Autozone, they have a IAC Node (actually several). The GM one I bought has bi color LED indicators. Kinda interesting to watch the colors change.

Point is with it you can verify the IAC controller (Stepper Motor Controller chip), and logic is in fact working.
 
Originally posted by Craig Smith
When you turn off the key with the FAST system, it will extend the IAC as far as possible. It basically just tries to shove it out for some number of counts that is more than enough in any circumstance for insurance. On power up the current position of the IAC is assumed to be zero.

Just dawned on me.
This is an invitation to trouble with condensation, especially in freezing temps.

Now the GM strategy of parking X steps open, makes sense.

Thanks
 
Excellent thought, Bruce.

Makes me want to see if we don't, in fact, open the IAC just a touch after we slam it shut. As far as I know, we just slam it shut and don't try to open it until the next time you crank the car.

If we don't, I like the idea of closing it fully and then opening it up 10 or 20 counts or so for just the reason you mention.
 
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