IAC Keeps Moving

69 1/2 Six Pack Bee · Post by **69 1/2 Six Pack Bee** » Mon Mar 13, 2006 2:35 pm

I tried to fire up the truck yesterday but first off I wanted to check the IAC (standard GM bolt-on type) position so I could get the baseline established. At first, when I powered it up, the pintle shot out so I was certain that the polarity was backwards. I swapped the wires and now the pintle moves inward. The first power-up it moved in. I let it set for a few minutes and it was in the same position. I then shut it off, powered it up once again and the pintle continued to move inward again this time bottoming out. I tried another IAC and go the same results. I have the default, 160 steps in the code and I have the "'IAC Moving Only" box checked. The coolant temp was @ 45 degreesF so then it should have moved 100 of 160 steps. I got the truck started and warmed up to normal operating temp today yet it did not move in the opposite direction. The IAC steps indicate it goes from 0 cold to 160 warmed up. I checked the coil windings prior to powering up so I know that coil "A" & "B" are wired in correctly.
WHat should I check?
This is what my settings are:

Thanx, Bud

TurboGt · Post by **TurboGt** » Mon Mar 13, 2006 7:33 pm

My gm IAC takes almost 290 steps to go all the way in. What you need to do is make it so the pintle is all the way out, then increase the start value (like 20 steps or so) and cycle the key each time to test. Do this untill the IAC goes all the way in with just one key on.

Right now mine is not starting at the same RPM, and I am still working on it but this sounds like your problem.

Good luck!!!!

69 1/2 Six Pack Bee · Post by **69 1/2 Six Pack Bee** » Tue Mar 14, 2006 7:56 am

I have changed the settings alot. I physically pull the pintle out and I can cycle the key on and off and it will just keep going back in regardless of the engine temp. I will try swapping some wires around.
Thanx.

Bernard Fife · Post by **Bernard Fife** » Tue Mar 14, 2006 8:17 am

Bud,

I'm not sure I am following 100%, but I believe in the later versions of the code the pintle doesn't extend until cranking starts (at which point it moves to the 'Cranking Position (steps)' before tapering to the coolant derived position when the engine is running). This was put in to avoid having the stepper miss steps while the voltage was pulled low by the starter motor. So you actually have to start the engine to see the pintle extend.

Lance.

69 1/2 Six Pack Bee · Post by **69 1/2 Six Pack Bee** » Tue Mar 14, 2006 2:02 pm

Okay, I'll back up a bit...I am running code V2.35 burned into an MS-II daughtercard atop an MS-I, V2.2 board. I am running the IAC via through the relay board. I have DB37 pins 25, 27, 29 & 31 jumpered from X11, 12, 13 & 14 and out to S1, 2, 3 & 4 respectively. I originally had it wired exactly as in this diagram:

I have since tried 16 different wiring combinations (utilizing the relay board terminals) and I will either get the pintle to shoot out or it will bottom out. I have tried several different combinations of start steps from 1 to 255. I have tried the different methods of running always, only moving, 15-minutes. I have started the engine and let it warm up completely...no difference. I get the steps to move at least as indicated in MT. I even went as far as to pull out a spare coolant and IA temp. sensors and plug them in to a warm engine to "fool" it and although the steps@ the current temp. correspond it does nothing. It either goes all the way out or I swap two wires and it goes all the way in. No, "start steps and then to the current step",...nada, zilch, nuttin' I have tried two different IAC's and they both respond exactly the same.
What am I missing here??

69 1/2 Six Pack Bee · Post by **69 1/2 Six Pack Bee** » Tue Mar 14, 2006 4:04 pm

I have searched through the past postings and I have found some interesting info. I will try increasing the step time to maybe 3 or 4 (from the default 2.5) and see if that helps. Also, I might, at the very last resort, do the resistor jumpering as described at length in several posts and also in the manual.
In the interim, if any of you guys can think of anything please let me know !!
Thanx!

krisr · Post by **krisr** » Tue Mar 14, 2006 4:20 pm

I wouldn't jump the resistors until you are 110% absolutely sure your wiring is spot on first. I had tested my IAC (inline GM plug style like yours) last night and found that I had to reverse the wires. Since i'm using the harness from DIY I soldered the wires on the PCB to suite the harness colours etc, once I got it workin I found it was working sporadically so I soldered the jumper on the MS2 board which seemed to fix that.

I shortened my Step Size to 1.5 and found it to be more responsive which was typical. I also found that my throttle body housing liked to have the last step at about 180 so my start steps are 200 to get it to retract all the way.

Not sure if it helps, hope so though...

69 1/2 Six Pack Bee · Post by **69 1/2 Six Pack Bee** » Tue Mar 14, 2006 4:51 pm

I agree about the "don't solder those yet" theory with you. What I get is just the pintle sits there....no movement after the initial move. The way I am reading it is that it goes to the full open upon power-up. Then it will move the other way to the predetermined steps that is the "start" position. Whatever you put in there for a start position. The fully closed should be a few clicks more than your preset start position so if I am reading this correctly, say it "starts" at 180 steps. (maybe three more than the actual of 177 it takes to close it all the way. Then, it will traverse the close direction that preset number in increments proportional to the coolant temperature until the pintle is bottomed out. If I start a warm engine, it will go all the way open and then back down to the fully closed position within a few seconds. I also understand the taper time from crank to run..that is easy.

I get the logic and the operation. I just don't get what the heck is keeping it from doing what it is intended to do. The wiring is sopt on as I have checked it numerous times. I have spent a couple of hours trying to sort this thing out

Bernard Fife · Post by **Bernard Fife** » Tue Mar 14, 2006 4:57 pm

Bud,

Are you starting the engine to see if the pintle extends? Because if the MS-II doesn't see an rpm signal, the pintle doesn't extend, it just sits there until cranking begins.

And jumping the resistors on the bottom of MS-II won't hurt if you 'mis-wire' the ordering on the 4 stepper wires, they are there to protect you if you accidentally short one of those wires to ground (which should be fairly easy to avoid). So if you are running the engine and not seeing the pntle extend, the next thing to do is jumper the two large resistors on the bottom of MS-II as described in the manual.

Lance.

m0ntecarloss · Post by **m0ntecarloss** » Tue Mar 14, 2006 9:00 pm

Dunno if this will be of any use but I figured I'd post anyway.

MS definitely needs to see rpm for the IAC to move back the other way after its initial power up. Megatune is an easy way to see what should be going on - when you start cranking you will see the steps move to your cranking position. So you can verify when it should be moving just by checking megatune and watching the IAC when the numbers change.

One unrelated thing I'd like to mention is there is one exception to the cranking position number that I found confusing and dont really like. If the coolant temp happens to be cool enough such that the corresponding IAC steps (from the table) is lower than your cranking position, that number will instead be used.

For example, say your cranking position is 160, coolant temp 45F, and in your IAC steps table 45F equals 100 steps. Then when you crank the cranking position will be 100, not 160....

This caused us a lot of grief in trying to get our small block started properly in cold weather. I am going to modify the code so the crank position is always the same.

Oh also FWIW for our setup, our start position needed to be 255 steps and we are using 160 cranking steps (GM IAC)