Return-to-idle tuning for a 2002 Corvette

[NSFW]

Thanks for chiming in!

It no longer dies, so that's a huge improvement. The MAF scaling curve seemed suspicous so I copied one from another tune that had the same sensor and tube diameter, and I'm pretty sure that was the key thing. However the MAF sensor is set to fail above 100hz, and has been since the cam install (which is when the problem started). Someone on ls1tech seems pretty certain that the PCM doesn't use the MAF signal so I dunno. But I've driven around town for an hour without the engine ever dying, where before it would die at every third stoplight. The return-to-idle isn't perfect, so there's more tuning to do, but I think it should be pretty straightforward.

Yesterday I put all of the DFCO settings back to stock, and return-to-idle was unchanged, so apparently that was not a factor after all.

Raising the base running airflow tables to around 13 g/s helped a lot in the beginning, but now that I have a logger I can see it idling at around 7 g/s so I'll be reducing the base airflow table next. The STIT PID isn't part of the SAE standard, so it will take some effort to get that working in the open source logger. But in the meantime I'm just going to try to get the logged MAF at idle to be somewhat close to the MAF configured in the base airflow table.

Reducing the idle spark table helped a lot, that was one of the first suggestions I got after I started asking around. It was running about 28 degrees when I got the car back from the shop, which apparently left no room for the spark adjustment to increase torque. Reducing it to 19 degrees made the idle much more stable. After that change and the increased base airflow, the car idled pretty well, it just wouldn't return to idle consistently.

The other thing I see now that I have a logger is that the fuel trims are maxed out at idle (+25%). So I'm working on adding VE to sort that out. And the rest of the VE table is kinda lumpy so I'm pretty sure idle area isn't the only thing that needs work. Knock retard is pretty rare, so it's not urgent, but it still bugs me.

I'm hoping that getting the fuel trim and base airflow right will fix the RPM dips that I sometimes see when the car is returning to idle.

[jlvaldez]

Good to know. Stit is extremely helpful for tuning your have airflow table, good pif to have. I think tech 2 can read it. Maybe that will be helpful.

If there's one thing I've learned with cammed LSes, is that you shouldn't waste your time trying to solve idle issues until you get your fuel tables dialed in. You'll Chase your tail and most issues are due to running a bit rich for some reason

[NSFW]

I got this pretty much figured out, and started a new thread to describe the solution:
viewtopic.php?f=28&t=6715

My clutch/flywheel is lighter than stock (33 pounds) and that was a big part of the problem. That required changes to the idle airflow PID stuff, and after that was updated, the throttle cracker and follower tables pretty much fixed the problem.

The VE table turned out to be mostly just a distraction because the car was not in fact tuned for SD. The previous tuner told me it was, and he tried, but he got it wrong, so it was still using the MAF full time.

[Ken]

Ive been chasing the same problem for a month now on a mates VY tune I've been playing around with.
11.6:1 comp, 233 / 242 @ .050, 112 lobe sep, 108 intake CL, manual, 4.11 diff.
I've got it destroying the tail shaft donuts within a month, economy's the best he's ever seen, drivability pretty close to factory, except for the idle drop off when the clutch pressed at low speed, and sometimes when attempting to take off too quick.
Below settings fixed the problem 100% for this tune..

[VK_3800]

How does it behave now, does the rpm hang significantly high or does it drop to a suitable level OK?

[Highlander]

The problem is the way the idle routines interact and they fight each system all the time. Its not a cohesive system like the Gen IV are. But they can be made to cooperate

https://www.youtube.com/watch?v=PQjWK3P ... e=youtu.be

236/252 113 cam 427 NW103mm tb.

[Ken]

How does it behave now, does the rpm hang significantly high or does it drop to a suitable level OK?

Yeah it drops to idle speed in expected decel time, doesn't hang or drop too quickly,even if turning when the clutch is pressed.
I'd played around with settings like "stall saver rpm' "throttle follower" "rolling desired idle speed"and "DFCO" with minimal difference.
In the "throttle crack airflow P/N"setting, originally there was no setting in the 3 kph line, was just zero, and the engine speed dropped to 750 rpm when pulling up, then recovered, then as soon as I added that one extra setting , all idle speed dropping problems were solved.
Before playing with any of the cracker settings, it stalled often, even if changing gears too slow at a slow rpm, or not sliding the clutch enough on take off.
it was only when I opened the edited binary with efilive to double check that the XDF entries I added actually worked that I noticed what the extra info stated in efilive regarding throttle follower, that I found that throttle cracker was also meant to be altered / functioning.

Text at bottom left of this screen below.

[VK_3800]

Thanks for the info, guess I'm trying to have my cake and eat it too as I'd like to keep the idle rpm under 1000 (cam 242/252 @.050, 112 sep). More things to try anyway, to the extent I can translate to 12P.

[Ken]

I've got this one idling at 1000, seems happy there, 1,100 for the rolling idle setting was part of what I was trying out to stop it dropping randomly before I found the throttle cracker setting fix.

[VK_3800]

You're talking about a V8? I assumed with 1100rpm rolling it would be more like 800 normal idle - seems very high for a small-ish cam? I've set idle at 850rpm, it seems to be happy with that but maybe I'm expecting too much for it to stay under 1000 at all times? (Apples and oranges since mine's a Holden V8 but would have though the LS would do better with good heads and roller cam).

My stalling issue might come down to an exhaust issue after all, I can stop it from stalling no problem by hanging the revs high above 1000 but its quite annoying. :-/