Stepper motor issues with homing steps and idle speed

[B1ack_Mi16]

IAC is still working fine (which were used when the chip went), I've tried both valves and (sadly) they act exactly the same.

The other components were not replaced, but DIYAutotune recommended it when changing the chip to make it more robust overall.
I'm no pro at all but I at least managed to change the chip.

[B1ack_Mi16]

BTW if I set it to 500 homing steps I ideally need to wait 500 x 3ms = 1.5 sec from I turn ignition on till I start cranking?

[billr]

True. And you also need to wait for the stepper to open from the homed position to the cranking position.

However, I'm not sure if the "homing" will continue even if cranking starts before the homing steps have been reached, but expect it will. If so, then it doesn't matter too much, you might just be a bit late getting to the cranking opening, maybe a bit of delay on firing.

[jsmcortina]

How does the stepper behave in test mode?

James

[B1ack_Mi16]

In test mode it moves very good at least when cycling in/out.

But of course I haven't noticed in detail if it actually jump one step if it is controlled to just move 1.

I think I'll start by waiting between ignition on and cranking, I might have been a bit fast in that movement of the key.

[kaeman]

I know this is probably a stupid question but,,,,, Did you actually do the test to determine the full open setting of the iac motor... I did the testing and mine gm stepper motor required about 170 steps to go from full closed to full open, I then added 15 steps to the count to force the stepper to fully close when first powered up, are you giving your stepper motor enough time to make it home before cranking up the engine... I am using the hold current setting, mine initial step size is 5ms and my step size is 4ms and my minimum steps is set to 2.
I had problems with the stepper that came with my Accufab throttle body not being repetitive in its operation, I called Accufab and they said that they had gotten a bad batch of stepper motors and sent me out one free of charge... it has been very reliable...
I was having the same kind of problems as you are suggesting before replacing the stepper motor. defects happen.. new parts are not necessarily good....
I would try changing out the stepper and see if your problems go away.

[B1ack_Mi16]

I know this is probably a stupid question but,,,,, Did you actually do the test to determine the full open setting of the iac motor... I did the testing and mine gm stepper motor required about 170 steps to go from full closed to full open, I then added 15 steps to the count to force the stepper to fully close when first powered up, are you giving your stepper motor enough time to make it home before cranking up the engine... I am using the hold current setting, mine initial step size is 5ms and my step size is 4ms and my minimum steps is set to 2.
I had problems with the stepper that came with my Accufab throttle body not being repetitive in its operation, I called Accufab and they said that they had gotten a bad batch of stepper motors and sent me out one free of charge... it has been very reliable...
I was having the same kind of problems as you are suggesting before replacing the stepper motor. defects happen.. new parts are not necessarily good....
I would try changing out the stepper and see if your problems go away.

Thanks for your input.

I did do a cycle test and such, but my thought was that the stepper is never supposed to be more than 90 steps out during cranking and never more than 45 steps open during warmup.
Hence when the engine is turned off the stepper would be somewhere between 0 and 45 steps depending on coolant temperature, and should ideally never need more than 90 homing steps if it moves reliable.

I did try several times to check what step size that seemed reliable and during test mode I found 2ms regular and 3ms on first step to be enough to get it moving reliable, but I upped it a bit later on without any extra reliability.

I'm letting it move single steps as 1 step actually makes a noticeable difference to the idle speed, so 2 steps as minimum would be a bit too eccessive I feel.

I'm having the kids this weekend, but next weekend I'll try to get some more testing done on the car again!

[billr]

Stalling steppers to find "home" is common practice with steppers of all kinds (not just automotive). It is the only way to get a reliable "0" count if there is not a limit switch or absolute encoder in the system; and will do no harm in a properly-designed system. Don't fight this trying to be cheap with the homing steps.

[B1ack_Mi16]

Trying to run it on Hold Current and 400 homing steps today and it seem to be much more stable in the operation. So maybe that was all that was needed.
Now I just hope the chip will not fail on me again.!

Thanks for all your inputs.

[billr]

Your main problem was probably not enough homing steps. Back away from the "hold" current for a while if you are worried about the drivers, see if that still works OK now that you have more homing steps.

[B1ack_Mi16]

Will give that a try next time I'm out testing indeed!

[Exidous]

I used Moving only and 417 homing steps with my GM IAC. 417 gives me about 5 steps of "preload". It does however stink to have to wait for it to move before starting. I could only manage 7ms so I'm at 3sec+ from key on to ready to go. I also has to swap wires around from what the LS diagrams listed. No matter what I did it was always doing the opposite of what I wanted. An increase in idle steps during warmup would lower the idle no matter what homing direction was selected.