ETC cars and IAC parameters

[Redline Motorsports]

It is obvious that GM utilizes the same PCM and OS's for both ETC and non-ETC cars. Why are there so many tables in the ETC cars that reference to IAC control? What is GM thinking about by still referring to an IAC that doesn't exist?

These are the tables that I would like to know there interaction, if any to a ETC's control;

IAC Effective area {4403}
Airflow Parked {4308}
Default IAC Motor Park Position {4401}
Maximum IAC steps {4402}

Anyone have any insight to the PCMS calculation process with these?

Thanks

Howard

[Chuck CoW]

Thanks for posting this Howard.... I've got an LS1 ETC car giving me a hard time idling...As soon as I fix one problem, I develop another.....

I'm not sure why idle control isn't (and wasn't designed) to be much simpler....

See what happens when you let engineers design things for the real world???

Anyway, it's usually not difficult like this car...but....It's hurting me....

Is there a way to limit the closing of the throttle kinda like the stop screw on a carb or t-body.....

The car idles great....but, For some reason, the throttle is permitting the idle to drop past the set point of 800 down to 4 or 5 hundred after opening the throttle.....It stumbles and then returns.... I've fixed this 1000 times before, but this thing won't cooperate.

any ideas....??? I've messed with EVERYTHING....and like Howard says,...There's a bunch of stuff labled IAC so how do we know if IAC applies to ETC or NOT....or when each is used by the o/s???

Anyone have any thoughts?

Chuck CoW

[trymyz]

Hey Chuck,
Have your tried slowing (reducing) the throttle follower decay. I found that this works for me.

[Redline Motorsports]

I can tell you that Chuck and I have been talking about this for a good three days which kind of stemmed this thread. GM really seemed to over complicate the "idle" function a bit too much! LOL!

The PCM should be smart enought to NEVER let the idle drop below the target idle rpm. Especially on a ETC car where throttle angle is in the control of the PCM. Unlike a F-body that requires a "minimum air rate" be set. This meaning that if you plug the hole in the IAC it should still have a non stalling idle.

We need some of the parameter hackers to drop in.............Jes.....

Howard

[DrX]

I believe that I was told previously that the IAC tables were not used on ETC vehicles. To confirm this I have tried setting B4403 to all 0's or all 400's while running on the RR and didn't notice any effect. I can log IAC steps but it is stuck at 310 no matter what values I put in those tables.

[Chuck CoW]

I believe that I was told previously that the IAC tables were not used on ETC vehicles. To confirm this I have tried setting B4403 to all 0's or all 400's while running on the RR and didn't notice any effect. I can log IAC steps but it is stuck at 310 no matter what values I put in those tables.

Tell me this.... Many of the idle settings rely on MPH from the pcm. But, after years of logging LS1's, My efi live scanner (and EFI LIVE dashboard) always report 36MPH even when I'm stopped....

I never cared, but....with the LINKING from the scanner to the editor trying to watch what's happening....The linking of MPH always stays stuck at 36....

What's up with that???

Chuck CoW

[jfpilla]

Tell me this.... Many of the idle settings rely on MPH from the pcm. But, after years of logging LS1's, My efi live scanner (and EFI LIVE dashboard) always report 36MPH even when I'm stopped....

I never cared, but....with the LINKING from the scanner to the editor trying to watch what's happening....The linking of MPH always stays stuck at 36....

What's up with that???

Chuck CoW

Try reducing the number of pids in the scanner.

[jfpilla]

Thanks for posting this Howard.... I've got an LS1 ETC car giving me a hard time idling...As soon as I fix one problem, I develop another.....

I'm not sure why idle control isn't (and wasn't designed) to be much simpler....

See what happens when you let engineers design things for the real world???

Anyway, it's usually not difficult like this car...but....It's hurting me....

Is there a way to limit the closing of the throttle kinda like the stop screw on a carb or t-body.....

The car idles great....but, For some reason, the throttle is permitting the idle to drop past the set point of 800 down to 4 or 5 hundred after opening the throttle.....It stumbles and then returns.... I've fixed this 1000 times before, but this thing won't cooperate.

any ideas....??? I've messed with EVERYTHING....and like Howard says,...There's a bunch of stuff labled IAC so how do we know if IAC applies to ETC or NOT....or when each is used by the o/s???

Anyone have any thoughts?

Chuck CoW

Chuck,
It's really not that complicated. Try this and do at fully warmed temperature to prove it.
Input the MAF g/s into the Desired airflow table.
You then want to get IACDES_B to be close to MAF g/s.
Raising ETC lowers the iacdes_b logged # but raises airflow and the opposite is true.
The numbers don't have to match perfectly and won't. It eliminates the change in behavior from what seemed like a good tune.
If you change the MAF or IFR enough after this it could affect the transition.
And best of all you may be able to put the stock cracker and follower tables back which then maintains consistancy with all other tables.
If you log a stock car you will find these results to be true.

[Highlander]

Raising it back from the grave....

Whatever happened with this Chuck... I am in this same boat right now. I have changed pretty much every single parameter available... My issue is pretty much as you describe it but its not consistent.

Aside to that... It will stall when moving the steering as the power steering takes a toll on the idle airflow... One minute is working fine and the next... it stalls... Fuel is steady and its fine...

I am using a 92mm throttle body and I am pulling my hair out. Idles PERFECTLY... You rev it and it will get back to idle correctly... but......... it stalls inconsistently with load... AFR and timing are pretty much where they can be... I have tried more timing.. less timing.. I can't command more than 46º advance which it "solved" part of the issue... but then again.. I had to revert back to 36º because i didn't feel comfortable since there was actually little room for correction when low idle speeds are achieved.

When getting to a street light... it can stall... it used to be because the throttle cracker doesn't decay when its disabled, it just goes to 0. PERIOD. Well... I zeroed the whole cracker table and the car will "idle" while rolling to ~1000rpms and wouldn't die... VOila... ok... after a while.. it doesn't want to do that... WTF! it is so inconsistent... There are no vacuum leaks or anything.. its just inconsistent...

This is a fast 92mm ported with an ls2 TB... I had this car idling perfect with its stock ported TB/intake and the 236/242 cam.

I need some light in this darkness....

[Redline Motorsports]

For starters did you tell the PCM that the throttle effective area has changed?

I would also look at spark timing as a well. The two things that effect idle stability are airflow and spark timing. If the desired airflow is correct I would look at spark correction as well as minimum spark at those areas. Try adding some spark to the cells below 600 rpms and also tighten up the allowable spark correction range.

The key to idle is to have just enough torque to overcome the engines friction but also just enough to keep the momentum going. Both air and spark are ones that effect that.

Not for nothing.............we have had nothing but problems with the FAST ETC TB's............only one we have had good experiences with is the TPIS unit.
Howard