IAC tuning. Am I crazy? (Solved!)

[bluetrepidation]

OK well I'm running 50 ohm coils here too. Now does anyone know the resistance for the "Jeep 4.0L IAC Valve" ? I see an IAC body to adapt older cars on DIY Auto Tune so surly this motor must run with no problems. I'm curious to know if the resistance of the coils is higher? Also is the jeep motor a permanent magnet type of stepper or an inductive one like GM is using?

Also the MS II board does not have the resistive network installed so the chip can detect the output current. Now granted a 50 ohm load only results in a 290 mA current which the chip can handle. But during motor movement current spikes could be overheating the chip or in some other way tripping the chip into fault mode?

Yeah my car still acted up on the way home. I left work with a high idle and suddenly I has no idle and stalled after coming to a stop. Somehow my valve is closing all the way even though it shouldn't be moving at all.

A.J.

[bluetrepidation]

How are you checking the voltage to the stepper motor? Just unplugging it and seeing if you have a voltage on any of the four leads?

A.J.

Bud;

Of course I'll share my solution, when I find it.

Update from last night. All indications have been that if the IAC motor needs to really go somewhere (ie 50 to 100 steps at a time) it works fairly well, however, if it needs to move just a few steps (ie 1 to 5 steps at a time) it doesn't work. In the idle steps table, with the engine at temp,
I changed the 160 deg bin from 200 to 100 and the idle increased, back to 200, idle decreased, 150 - idle up, 200 - idle down. Worked as advertised. Then took the bin to 150, idle up, down to 149, 148, 147,... to 200, no change in idle. Checked voltage to IAC, no voltage. Checked IACEnbl on the UDN2916LB motor driver, it was still enabled. Conclusion, the 2916 is going in to some sort of fault mode.

Question for the Gurus: The component values for the oscillator RC network on the 2916 are out of the range specified in the Allegro 2916 datasheet. Could this be an issue?

Scott

[bluetrepidation]

I dunno guys I'm really stumped. All I can think of is does anyone have a successful stepper IAC setup and can you share what kind of stepper and the settings you are using? What is the resistance of the coils?

I just played with my car for 2 hours and I can definitely say the motor doesn't respond to single steps. I plugged in my spare motor and as the engine warmed I noticed some steps are good and strong and others are very week. I just pressed my thumb down hard on the plunger and you can tell. Also sometimes when taking single steps I noticed the idle increase slightly when it should be decreasing.

Something is up.

A.J.

[Bernard Fife]

bluetrepidation,

I had one behave like this a while ago - it worked sometimes, but was erratic and it seemed to depend to some degree on how hot the chip was. It turned out I had fried one of the UDN2916LB drivers, probably with static discharge (though I don't know for sure).

On the 'scope, with the stepper disconnected, on S2 (1B) I got a clean square wave, BUT it was 2 Volts to 8 Volts instead of 0 to 12 like the other outputs. If I connected a stepper, the wave got ragged. If I swapped to a different stepper, S2 still looks ragged, so the behavior didn't follow the stepper. So the 1B output could produce an appropriate signal, but only at no (or very low) loads, not with an actual stepper.

All appeared to work well if the MS-II got rpm signals in a reasonable amount of time, then the stepper chip stayed cool (~130°F) and worked reasonably well. However, if there was no rpm signal for a whle, the stepper chip got quite hot (up to 223°F). So you might check your stepper chip to see if it's getting hot when there's no rpm signal. If it is, then one or more of the drivers may be fried.

On close inspection, the chip appeared to be properly centered over the solder pads, and properly soldered. Under a magnifying glass I saw no signs of heat damage (like burnt traces or browned components).

I haven't replaced that chip yet (I use that MS-II for testing other things, and have had no further problem with any other MS-II), so I couldn't say how hard it would be to replace the stepper driver, but it is not extremely fine pitch. I beleive it is 620-1119-ND, for $3.89 from Digi-key (you should verify that number though).

Lance.

[Ballistic]

I don't know the cause, but the symtoms I've experienced have been much the same as others have described, where slow stepping results in missed steps.

A work around I came up with was to set the hot idle with the IAC fully extended and then adjusting the throttle blades to achieve the desired idle speed. Then, in the highest temp bin I set a number about 50% larger than the number of possible steps. As the engine warmed up, the rate of change from 160 to 180 degrees was enough to cause the IAC to fully extend. Over time though, as carbon builds up in the throttle body, the idle does get slower, thus it seems the need for some feedback control.

A possible software based approach I thought of would be to add some "stickiness" to the IAC movement, so that it wouldn't move until 5 or 10 or so steps were called for, and then moving those steps rapidly.

[bluetrepidation]

My chip does get warm but not hot in any way. I will check to see what happens with no RPM signal though when I get home. So Lance does anyone have a operational setup with a GM style IAC? Seems like lots of people are having problems. It would be nice to compare some of the motor styles that work well with those people have more problems with. Settings too..... The fact that I'm wasting this much time on idle control and can't move on to tuning more important things like my VE table is driving me nuts!

A.J.

bluetrepidation,

I had one behave like this a while ago - it worked sometimes, but was erratic and it seemed to depend to some degree on how hot the chip was. It turned out I had fried one of the UDN2916LB drivers, probably with static discharge (though I don't know for sure).

On the 'scope, with the stepper disconnected, on S2 (1B) I got a clean square wave, BUT it was 2 Volts to 8 Volts instead of 0 to 12 like the other outputs. If I connected a stepper, the wave got ragged. If I swapped to a different stepper, S2 still looks ragged, so the behavior didn't follow the stepper. So the 1B output could produce an appropriate signal, but only at no (or very low) loads, not with an actual stepper.

All appeared to work well if the MS-II got rpm signals in a reasonable amount of time, then the stepper chip stayed cool (~130°F) and worked reasonably well. However, if there was no rpm signal for a whle, the stepper chip got quite hot (up to 223°F). So you might check your stepper chip to see if it's getting hot when there's no rpm signal. If it is, then one or more of the drivers may be fried.

On close inspection, the chip appeared to be properly centered over the solder pads, and properly soldered. Under a magnifying glass I saw no signs of heat damage (like burnt traces or browned components).

I haven't replaced that chip yet (I use that MS-II for testing other things, and have had no further problem with any other MS-II), so I couldn't say how hard it would be to replace the stepper driver, but it is not extremely fine pitch. I beleive it is 620-1119-ND, for $3.89 from Digi-key (you should verify that number though).

Lance.

[Bernard Fife]

So Lance does anyone have a operational setup with a GM style IAC?

bluetrepidation,

Yes, absolutely, which is why I can't help much. Mine works, so it's very hard for me to make suggestions for those it doesn't work for. I have used 3 different 'square' connector GM IACs and the two different 'in-line' connector IACs, all work for me as expected (excepting the blown IC issue I mentioned above).

I did find I had to jumper the resistors on the bottom of the MS-II board, and I also had to experiment with the number of steps to get reliable operation in the car. These are detailed in the docs.

Lance.

[JSC]

GOOD NEWS;

I changed the components on my MSII board this morning and for the first time the IAC stepped in a few steps at a time on warn up. It brought the idle down slowly as it warmed up, seems to be working as advertised. I'll play with it more today and report in the morning.

Scott

[bluetrepidation]

Alright, I ordered a new chip today. I changed my habits and noticed something. Instead of letting the MS sit in an on state while I tinkering with settings I immediately start the car. I noticed that the idle doesn't act nearly as erratic then it does letting it sit with no RPM signal like you mentioned. So I'll get back to you when I get it installed.

A.J.

So Lance does anyone have a operational setup with a GM style IAC?

bluetrepidation,

Yes, absolutely, which is why I can't help much. Mine works, so it's very hard for me to make suggestions for those it doesn't work for. I have used 3 different 'square' connector GM IACs and the two different 'in-line' connector IACs, all work for me as expected (excepting the blown IC issue I mentioned above).

I did find I had to jumper the resistors on the bottom of the MS-II board, and I also had to experiment with the number of steps to get reliable operation in the car. These are detailed in the docs.

Lance.

[bluetrepidation]

That is GOOD NEWS. Let me know how things run. I'll be trying the same thing soon.

A.J.

GOOD NEWS;

I changed the components on my MSII board this morning and for the first time the IAC stepped in a few steps at a time on warn up. It brought the idle down slowly as it warmed up, seems to be working as advertised. I'll play with it more today and report in the morning.

Scott