Idle fine tuning problem LS3 on 0411

[Tnsejed]

Seems I've chased my tail for too many days on this and I need help.

The truck was tuned by myself and Ed remotely starting about 2 years ago. We got the VE, MAF, tranny, and Blend done very well (2% VE just about everywhere we could get). I've worked the spark table about a dozen times but without dyno MBT. Also got it to idle pretty decently but the idle was never tuned as we did not get there before the remote learning was unable to happen anymore. So I was on my own. It did everything pretty decently. I'm tuning this at 8500' elevation. The truck has been as high as 14000' on the trial without any hiccups. In the big rocks it does well.

Idle was ok for all intents and purposes but it never felt as happy as it should. The IAC numbers were really weird but came that way from the company who provided the engine, TB, harness, and ECM. The ECM had nothing in it other than a standard Fbody tune, BUT the IAC numbers did not match anything stock. So we figured we'll deal with that later as the range provided did seem to work. Although weird timing additions and STIT LTIT was happening etc.

This setup is in my crawler. Sealed GMPP 430HP LS3 (stock with F body exhaust manifolds). Running off a Tilden 102mm cable throttle body. Mated with a 2wd 4l80e (standard 2wd and operated as such even though its mounted to a 3 speed Tcase). Full hydraulic steering on 42's (hence the need for good idle characteristics with some rpm (775 goal)).

I've been chasing my tail with LTIT's etc for about 6 days now. Also tried adjusting IAC range to something closer to stock. I believe I was not waiting long enough for cool down and trims were going all over the place. I had gotten in-gear pretty good for awhile and then it all fell apart. There is some funkiness and I believe some of it is due to the manual engine OS segment swapped with auto trans. In the scanner I have full PRNDL being seen as well as current gear shifting using none. I'm not too hung up on this right now.


Attached tune is where I am at currently. The log is full idle in Park to temperature.

[Tnsejed]

I'll revise with a few questions I'm hung up on. Setting my LTIT in park while the engine is in an overspeed condition , and pulling timing, does not make sense to me. My head might not be wrapped around it good enough.

-I believe I need to set the correct iac idle position first. Which everyone seems to shoot for 60-80, but what about at altitude?
-After that, if the idle RPM in park is high, while pulling timing. Should I use the VCM scanner controls to bring the idle to where it needs to be (via possibly closing IAC) to log desired airflow?

RussK scanner channels is a non working config for me btw (scanner error), but I should have everything logged and the histo's I need to.

[Tnsejed]

Adding the in Gear log from cold up to temp. Fans off. I zeroed out the min max adaptive airflow in the tune as well.

One of the issues I encounter and have been fighting for park is the IAC jumping positive when put into park. I believe this may be one of the root problems. With this IAC step change. It never used to do this and I must be missing something.

This only happens with the IAC steps put to a more normal range (0-310). Instead of the 0-50 range it was from the get go.

LTIT is high and I can paste that (although its weird how it is more flatlined instead of a gradual curve).

[mbray01]

it doesnt happen to have a holley iac on it does it?
I have found that iac to move waaaaaay to slow, as well as not properly reset.

If its the holley Iac, id put in a factory style(will require rewiring as its wired differently)

[Tnsejed]

it doesnt happen to have a holley iac on it does it?
I have found that iac to move waaaaaay to slow, as well as not properly reset.

If its the holley Iac, id put in a factory style(will require rewiring as its wired differently)

That's a good question. I'm unsure whose IAC is in this throttle body. It is very similar looking to OE IAC for LS1 applications. Silver can with double dimples. EDITED TO ADD: Just ran out to the shop, appears to be OE (assembled in mexico on the female connector). Harness work is not an issue at all if that's what it needs.

To my eyes this IAC is commanded pretty slow, and It almost feels like it moves the pintle slow. But I tell myself its a 20 year old design.

I could pull it out and use the bidirectional controls with a dial indicator on the pintle and check for reset consistency.

Did something in the logs catch your eye on this? End of the second in-gear log I went from gear to park.

Thank you for your response!

[mbray01]

I would possibly try another iac, just to see. Nothing worse than spending an immense amount of time chasing idle problems only to find a bad iac, or a dirty throttle body

[Tnsejed]

I would possibly try another iac, just to see. Nothing worse than spending an immense amount of time chasing idle problems only to find a bad iac, or a dirty throttle body

Roger that. I've got a delphi one coming. Will be here tomorrow. Part of me wonders since the truck was originally tuned using 0-50 IAC steps, thats all it saw. Park position was at 50. It ran like that for 2 years. Now I'm telling it to use more of its range to tune the idle. It may be fubared. Will update tomorrow.

[Tnsejed]

Update. Swapped in the Delphi IAC. The in-gear idle trims over multiple starts, and IAC position showed me good repeatability. Re-enabled park/nuetral position adaptive airflow parameters and the gear to park IAC counts were reacting correctly (according to the scanner).

I'll also say the new IAC feels much quicker. The engine reacts quickly during initial park position startup.

Of note is the old IAC is also a Delphi IAC. Unless its a knockoff with the same delphi part numbers on the outside of the plug.

Anyways, time to log and get the trims inline.

Thank you for your help mbray01.