IAC tuning. Am I crazy? (Solved!)

[Joethemechanic]

I'm also having the exact same problems as you guys.

GM IAC seems to work fine if moving in large steps, but small steps is another story. Hot start works fine, cold start and I'll end up with too high of an idle.

Let me know if you want me to try anything. So far all I've done is jumpered the 2 resistors...this seemed to help but it's still not good enough

Ok, a few more cold statrs under my belt, Mine is also doing exactly the same thing.
If I just start it and go Idle only comes down to ~ 1200, I have to cycle the key once its warm to get it to fully close the IAC.

Mine also is a brand spanking new motor.
I also am runing the relay board, I will also try to jumper the polyfuse. I wonder if it is this pollyfuse causing My resets/stalling sometimes shortly after start-up?

[bluetrepidation]

I lifted phase one and jumped it to the phase 2 output. Both phases strobed correctly once I did this. Now I inverted one of my scope strobes and things got funky but it didn't look anything like the half step issue. I also ruined my MS II board doing this. So I'm thinking maybe I'm just doing something wrong here. I dunno. I'm tired and frustrated. I'll put this on the back burner till I get my new processor in. All I know is I'm not connecting my new card to the stepper motor till I comb through everything I can. So if anyone has any ideas let me know.



A.J.

[Joethemechanic]

Sorry to here about your board man, that sucks.

I jumpered the polyfuse on My relay board, I was whishfully hoping it might cure a stubborn intermittent reset issue I am still fighting also. I also used the occation to recheck all of the connections.
No go, first thing it was reset and loose comms....

In any case it still has the IAC problems. I got it started and it warmed up, IAC counter went up to 200, still idling @ 1200 or so. I blipped the key and it came right down

I also jumpered the two large resistors on the MSII card.
I did notice that changing the control to moving only " seemed " to let it make small steps, as I watched the counter slowly move up I could here the pitch of the air bleeding past the IAC, as well as the general engine noise, Change in time.

However.... it still did not come down as it should have, again had to blip the key to get it to settle down.

Don't get it, I though MSII code was bulletproof
Joe MSII 2.35 V3 GM HEI-TBI 406sbc.

[Bruce Bowling]

OK, I am just seeing this thread for the first time here...

I will bench test a few things with the IAC, but I want to try to separate the issues here:

1) Is everyone with issues using a GM IAC, either the inline connector or the square one? Or are these other stepper types? If so which ones?

2) jumpering out the big resistors, does this have an effect?

Al will check the code for miss steps. For the RC components and the response from Allegro, the resistor/cap range specification apparantly is something added to later data sheets. The stepper motor circuit was the one used on the EFI332 designed almost 10 years ago. The R value used was much lower (1K) and was adopted in other circuits that used this chip (for example see http://www.geocities.com/researchtriang ... _schem.gif).I personally know a few individuals over at Allegro, I will contact them directly on this.

Jumering out the large 1 ohm resistors will totally bypas the whole RC thing because the part never goes into the hysteretic current limit. The part should then be just a dual h-bridge w/o current limit.

[krisr]

I have the same problem with my O-Ring stepper IAC. It is VERY sporadic but I had decided to ignore the problems for the time being and disable IAC to continue tuning as my car will fire/idle happily from a dead cold start with no throttle assistance/IAC. Also my 400 has a rather large overlappy cam too.

Bruce, FYI my IAC is an inline plug o-ring stepper with 50ohm coils.

[Joethemechanic]

Bruce,

1) Is everyone with issues using a GM IAC, either the inline connector or the square one? Or are these other stepper types? If so which ones?

Mine is a brand new square GM style. And if I read the thread correctly, most of the others are GM style, square or flat.
I cant say for sure if jumpering the resistors helped, because at the same time I set it to MOVING ONLY to be safe, as the chip was getting warm enough ( though not hot ) on ALWAYS ON .
that seemed to let it make smaller steps, but I was judging by ear, not exactly scientific ( but I do have an exelent ear! ) . It still did not function properly though.
I have a large datalog I would like to show you, however I have reached My download limit and am unsure of how to reset it.

Thanks Bruce,
Joe MSII 2.35 V3 GM HEI-TBI V8 406sbc
Thanks

[BottleFed70]

OK, I am just seeing this thread for the first time here...

I will bench test a few things with the IAC, but I want to try to separate the issues here:

1) Is everyone with issues using a GM IAC, either the inline connector or the square one? Or are these other stepper types? If so which ones?

2) jumpering out the big resistors, does this have an effect?

Thanks for looking into this Bruce.

I've been having the same problems as mentioned earlier. GM Stepper IAC seems to move fine when sent large steps like in a hot start. But doesn't end up moving enough when sent small steps like during engine warmup.

I'm using the GM stepper IAC with the Inline connector or "o-ring" style. I measured approx 47ohm accross the coils.

Jumpering the resistors seemed to help a little, but it's still far from stable.

[Philip Lochner]

1) Is everyone with issues using a GM IAC, either the inline connector or the square one? Or are these other stepper types? If so which ones?

2) jumpering out the big resistors, does this have an effect?

Bruce

1) The IAC I'm using on my Land Rover has a square connector and LOOKS the same as the one on the left at http://www.megasquirt.info/ms2/IAC.htm in all respects.

2) I can not accurately answer your second question as I've also changed my algorithm from "Moving only" to "15 Min IAC" which seems to work better.

3) My IAC does track the Idle steps but ONLY once it decides to move. With cold starts it seems to stick in the open position. Three minutes or so later if I restart the engine it starts tracking Idle steps. OEM ECU had no problem operating the very same IAC even before I cleaned and lubricated it as well as it could be.

4) Next: Certainly not the primary issue at hand but still relevant. I can NOT get the "Time based after start" on the "idle control" page to work - at all. My MT is set up for Deg C. I have noticed the WUE coloured blocks and Black arrow tracking the bins as if they were in Fahrenheit. I am wondering if this same issue is not affecting the "Time based after start" function or perhaps in general.

[bleoh]

[quote="Bruce Bowling"]OK, I am just seeing this thread for the first time here...

I will bench test a few things with the IAC, but I want to try to separate the issues here:

1) Is everyone with issues using a GM IAC, either the inline connector or the square one? Or are these other stepper types? If so which ones?

I am using a stepper from a 1993 Jeep 4.0 motor. It will open to the cold start value and stay there until I restart.

2) jumpering out the big resistors, does this have an effect?

I have not tried this.

[69 1/2 Six Pack Bee]

I had the inline "o" ring GM stepper. I had jumped the resistors, tried all of the algorithms and many, many different combinations of step start counts, closing counts, temperature curves and all to no avail. I had replaced the cap and resistors that JSC had suggested and I could not honestly tell if it made a difference primarily because I was trying to tune out an ignition related issue when I started it up. I had decided to say to heck with it and I quit.

I could not tell conclusively if the component swap had resolved anything prior to removing the MS system entirely.

I am certain you guys will get to the bottom of this.
Good luck!

Bud