IAC control...code revision?

[S.Bretz]

I remember there being an issue a while back with some of the older code and IAC control. The IAC would stop working after a short period of time...30secs....60secs...something like that.

I seem to be experiencing a similar issue. I can start the car and observe another IAC in a t-body. It will only move when i crank the car. If I play with the IAC step table, I get an bunch of nothing..


I was wondering if any one remembers the fireware code that had issues, and which code fixed it.

[grippo]

Other than at key on, the IAC shouldn't move unless coolant temp changes.

There was an issue with some IAC motors that would not respond to single step change commands, so code was put in to allow the user to set a min no. steps to move at a time. This was done somewhere prior to 2.864 code.

[S.Bretz]

Hummm.It does move on start-up...but that's it.

I turned the min steps to 5. Hyp is set low so that I can get change updates faster....but it always does the same thing.
Same thing being that it will idle up to 3K and it won't change...no matter the crank/table values. The only way for me to get it backdown is to use an OTC IAC motor tester that we have at the shop.

[grippo]

OK you are saying you start up a cold car and the stepper goes to the starting position and then as the car warms up the motor never moves. If you set up a step gauge on the PC or do a datalog, do the commanded steps change with coolant temp ? If they do and the motor doesn't move, then set the min steps to something higher than 5 but less than the max change you expect from your step vs clt table. If it still doesn't move I don't know what to tell you - I can only try your msq. If the commanded steps don't change on the gauge or datalog, then that is a configuration problem and I can check that with your msq. Did this ever work or does it work some days and not others ?

[S.Bretz]

I can watch it change on the MT gauge, but there is no effect on the idle speed.

It also doesn't seem to make any difference what the crank/cold start postions are. It always opens it enought o rev up to 3k.

I thought I might have had the iac wired reverse, so I got the other t-body to hook up and watch. I can see the plunger open all the way up, then come back down...always to the same spot. I can't determine if its wired backwards because I can't see it mover after ti does the crank position stuff...and when it does that, I'm not sure which way its suppose to move first, but I do have movement in both directions. Should it pull open first, then close back up, or should bottom out on the set first and the pull back open?

BTW, this is a moving only stepper on a GM LT1 t-body. I aslo used a saturn stepper to test with. Both have the same internal wiring, both motors have resistance within 1 ohm (53-54ohm).


I'll try to play

[grippo]

When you first turn on the key you want the motor to bottom out on the stop or seat - that is to retract. This is the only way the computer can tell where the pintle is and it should be consistent every day because the seat will always be where it is. After it is at the seat, which it now calls step 0, it should move off the seat to a new positive position that depends on the coolant and what step inputs you specify.

If the steps are changing on the gauge I doubt this is a software or software config problem. The only way to be certain would be to scope the outputs and see what they look like at key on and then see if there is the same output every time the step changes on the gauge.

Is it possible that if the motor spins out away from the seat at startup it gets stuck, and while your OTC motor tester is strong enough(can source enough current) to pull it back, the chip on the processor can't ?

[S.Bretz]

Is it possible that if the motor spins out away from the seat at startup it gets stuck, and while your OTC motor tester is strong enough(can source enough current) to pull it back, the chip on the processor can't ?

Interesting conjecture. I'll have to look into that.

When you first turn on the key you want the motor to bottom out on the stop or seat - that is to retract. This is the only way the computer can tell where the pintle is and it should be consistent every day because the seat will always be where it is. After it is at the seat, which it now calls step 0, it should move off the seat to a new positive position that depends on the coolant and what step inputs you specify.

hmmm... I think I might be backwards. It pulls all the way back, then moves forward to set the crank pos. I'll double check to make sure that is the case.

As far as it being an firmware issues...I know now that it is not. I remembered there being an issue in the past and it was resolved. I was trying to make sure my 2.884 was NOT effected....to save my self from chasing ghosts.

[S.Bretz]

Well, I got it to work...sort of.


It seems the some confused person wired the IAC motor backwards. When it was suppose to be going to the seat, it was pulling open until is got suck.

I rewired it and it moves the proper directions now. But it doesn't update the pintle when its cold. The gauge will update, but the pintle doesn't move until the engine gets warm. This morning, when cold it continued to idle high from the "guess points" that I entered last night (after the engine was hot). I had to pull over this morning and cycle the power off and restart the car to get the cold idle postions to change ( I was moving the tuning point more the my min. movement position). But once it gets to operating temp (180-185 F) I can move that tuning point up and down and it responds as long as the change is more then the minimum change value....so more tinkering.