Today, the engine started immediately when cold, started idling down and then shut off. I decided to spend some more time playing with the stepper motor. I pulled it out, left it connected and played with the software controls.

If you listen and watch, the motor tells you what you need to know for step count when you power up. Too many steps entered into the control software cause a vibration at the end of one cycle and too few steps cause the same vibration at the other extreme - either retraction or extension. I found that with the way I have it wired, there are 98-100 steps, depending on hysterisis influence, so I set the step count to 100.... a big change from the MS default values for GM steppers.

Then I played with the Time Step Size and found 2.7 milliseconds to be ideal at first. The motor liked that until I reinstalled it and the engine was running. The engine didn't react as I expected, so I pulled the motor out again and found that when warm, it needs a longer pulse for reliable operation. I found 4.0 milliseconds to work fine when warm. This number should be kept as low as possible, still giving reliability.

I played with the IAC step counts and afterstart enrichment some, but then the idle was high and didn't react as I expected..... so I generated a new VE table which resulted in higher values. I now have it idling at 650 rpms and it starts ok when hot. I think the stepper is under control, but I'll see what it does tomorrow.

I tried playing with auto tune in the idle bins, but got the "tuning point is outside window" message. What does that mean and what should I do about it?

Frank