IAC, dosn't close from cold start.

[Buick pwr'd Brit]

Now that the weather is nicer, it's time to take another crack at tuning my IAC.
What is happening, is the IAC will not close completely from a cold start after the engine is warmed up. After the engine is warm, I can cycle the key off, re-start, Idle speed will then drop down to curb idle ok after a few seconds like it should.
I must be missing something in my settings, that I havn't tried yet?
My set up 3.5L V8, supercharged, MSII code 2.881, GM stepper motor with the flat 4 connector.
IAC Stepper Moving Only
Time Step Size 2.0 msec. (have tried settings up to 6.0 msec)
Acc step size 0.0
Min # steps to move 1 ( I have tried up to 7)
Start value 160 ( have tried 100 through 200)
Cranking Position steps 120 ( have tried 40 through 160)
Crank to run taper time 5 sec
Hysteresis (F) 5.0
Time based afterstart
Cold temp 0.0
Cold position 120
Cold taper time 40
IAC tuning steps currently at 40@-40* through 180@160*, I have set the 160* warmed up value as high as 300 steps, in an attempt to gain more time to force the IAC closed.
Also did the jumper accross the resistor on the daughter board. When I make some of the changes listed above, it will change cold idle rpms. However it still will not come off of high idle completely untill I do a key cycle with the engine above 160 degrees. I have tested the IAC motor in a spare throttle body, it does have full movement. Kinda running out of ideas?!

Bill

[Philip Lochner]

Bill

You're not missing anything. IAC control, although almost there, is not quite sorted yet. It seems that when MS sends pulses to the IAC to turn, not all of them are physically translated into actual IAC movement, thus "missing" steps. This results in not all the steps being executed when it has to gradually move to the closed position. When you do a restart when warm, it executes all the desired steps in one burst thus missing very few, if any, steps and your idle is normal.

ALL the rover engines I've done, this happens.

Here are a few suggestions:
1) Increase the minimum step count to say 5 or 8. This means the IAC will only move in a few bursts of steps as set by you, thus missing less of the total amount of steps to be done;
2) Close the base idle screw more (if you still have one) so that IAC does not HAVE to fully close. This way the engine will hopefully be less sensitive to a few steps being missed.
3) Try the MS-2/Extra R2 code. This has CLOSED LOOP IAC control and it seems that it does work. I still want to try this on my car.

[bleoh]

Try a start values higher then 200. With my Jeep IAC I am at 250. I have been using minimum stepp # of 4. I had trouble with earlier codes and before jumping the resistors, but it has been rock solid for me for a while.

Brian.

[Buick pwr'd Brit]

Phillip
I increased the step size to 8. It seems to be operating better now. I'll have to do a few more cold starts to be sure. Takes a bit of time, making an adjustment and waiting for the motor to cool all the way down!
Brian
I havn't thought about "shifting the scale" up into 200 range. If it continues to be a problem, I'll give it a try though.

Thanks guys
Bill

[jimchristiansen]

I've been at the same place as you with my IAC for my 350 tpi setup. I have purchased a new IAC (used one was seized) that cannot be turned by hand and am using "on for 15 min...". I've had most luck with 300 steps with most starts "normal" now...

I also have set "Fuel Setup > Idle Control" the total start steps to 300 as well as "Other Tuning > Idle Steps" to 300. Are these set to the same for you?

Please let me know what works for you in the end.

[Philip Lochner]

that cannot be turned by hand

Youre not supposed to be able to turn it by hand. If you can, its broken.

[Buick pwr'd Brit]

Jim
Still kinda messing with it. One thing I did notice, if I narrow the spread size between the high and low settings in "other tuning idle steps" it helps a lot.
When I increase the cold fast idle #s, so the cold idle isn't as high, it will work correctly most of the time. I believe it's because the IAC stroke is not as long, therefore it has less distance to travel in the amount of time given.
I think this is why the higher numbers are working for Brian.
Since I only need 1300-1400 rpm for a cold idle, I've gotten away from using a linear warm up table. Seems to work better if I fire it up cold, then enter the desired step sizes as it warms up.

Bill

[89jyturbo]

I've installed two systems with GM flat 4 IAC valves. Both had the issue described on older code versions. When I switched them over to 2.88, I set the 'Min Steps' to 10 and in both cases the IAC functioned perfectly. I have a third install running the square 4 GM IAC and that has no problems on 2.6 code (this valve seems to be less sensative to 'missed' steps).

[jimchristiansen]

Thanks for the info. I'll increase the min step to 10... I think I've got it at 5 or 8. Regards, Jim

[Buick pwr'd Brit]

I set my min step size to 10 last week. So far it's worked correctly every time!

Bill

[jimchristiansen]

I set my min step size to 10 last week. So far it's worked correctly every time!

Bill

Yes, I'm at 10 with better results, too. What are you running for "Time step Size msec" ?

Jim

[Buick pwr'd Brit]

Jim
It's currently at 2.0. If the IAC continues to work correctly, I'll most likely leave it there.

Bill

[jimchristiansen]

Jim
It's currently at 2.0. If the IAC continues to work correctly, I'll most likely leave it there.

Bill

Hi Bill,

I was at 5 msec and have just peeled it back to 4. I'm paranoid of burning out those little coils... Knowing yours is working at 2 gives me incentive to keep whittling it down. My first IAC was shot, so in trying to get it working my msqs slowly had that msec count increasing trying to get it working... Now to pare it back down I suppose.

Thank you, Jim