Over/underspeed made it worse

[EFI]

So I have an h/c/i LS2 with a fairly tame cam, mid 220s 112LSA 2.5* overlap.

Been trying to nail down the idle and had it pretty good but still saw huge jumps in timing (mainly down). Idle is set at 26* but saw as low as 16*.

Saw a few threads suggesting messing with the overly done over and underspeed tables. Most of them suggested halving the data and then interpolating between the ends. I did just that and after I flashed the new tune it seems to have made it worse. The RPM swings are much much bigger now and I still see the same exact timing drops. So it made no change in how the timing acted, but made the car idle alot worse.

Did I do this wrong somehow? Or are these tables not really to be messed with?

I have 2 long logs that I did, one with the good idle and one with the bad idle that I can upload. But they are long long logs with driving all over so not sure if anyone really wants to sit and dissect those. I have however did some graphs in excel with the data and you can see the idle RPM and how different they are.

goodidle.jpg

badidle.jpg

[SultanHassanMasTuning]

what you need to work on is your BRAF table, if you are inducing too much air your over/under will react.

say your base timing is 21 degrees now, and you have dialed in your BRAF and logged timing is say 10. means you need to rework your BRAF table and reduce it a little at a time.

[EFI]

Hmm I thought I had the RAF table pretty well dialed in.

For example: no matter how low I set the commanded idle and minimum to, it will only go as low as 691 average. So this tells me that the airflow is just about right for 700, if not a little low.

So what should I do? Put the over/underspeed tables back to stock and go lower my RAF tables or try and work those with the current halved over/underspeed tables.

[SultanHassanMasTuning]

post your tune there are a few other changes if your timing is what your after

[EFI]

Here's the file. It's not so much the timing that I'm after...just want to nail down the idle and I figured large timing swings can't help. Or do they as in that's how it keeps the idle and I should let it change timing as much as it wants?

GTOTune.hpt

[SultanHassanMasTuning]

under diagnoses disable Catalyst test, also do you have a log?

[edcmat-l1]

26 degrees of timing is too high for that cam. I'd try it at about 18 degrees.

Use your scanner VCM controls to figure out where the idle spark needs to be. It's also a good way to figure out if the idle airflow is high or low.

[mowton]

Tip -- Set the idle timing to give you the most vacuum (lower MAP)

Ed M

[Gelf VXR]

Tip -- Set the idle timing to give you the most vacuum (lower MAP)

Ed M

And retard a few degrees to allow min max spark tables to do their business

[MikeOD]

Tip -- Set the idle timing to give you the most vacuum (lower MAP)

Ed M

Not a good idea on a drive by wire car. The throttle plate reacting to correct idle will result in bigger RPM swings.

Set your idle timing a good deal lower than peak vacuum to allow spark advance to be able to correct it before the car needs to move the throttle plate.

[EFI]

So I've been able to get it to idle @ 650rpm pretty well. However I can get to this two different ways:

- Set the commanded idle at 600, but because the airflow table is high it only goes as low as 650. But since it's 50rpm higher than commanded, the overspeed table is constantly pulling timing 5-6* to keep it there.

- Set the commanded idle at 650, and since the airflow table is right on the money it stays at 650. This way it also maintains the commanded timing and rarely does it need to over/underspeed correct.

Both of them seem very stable, just one runs slightly less timing and the only other difference is dynamic airflow (which is lower in the first version). The rest (kpa, torque, fueling etc.) is the same.

Which way should I do it? One where it constantly tries to keep it by timing swings or the other?