Engine surging with light throttle

I'm experiencing a problem I have never encountered.

The background info: I ported my TB some months back but I got into the idle control area due to my over aggressiveness. No big deal, I just lived with the slight idle surge and allowed the ECM to pull a little extra timing to try and control it. I finally picked up another TB and decided it was a good time to scale my tune. Now, I am experiencing and off-idle surge of about 200 RPM. The scanner shows and idle ETC% of about 10%. Now at frame 1280 in the attached log, you can see I give it a little throttle and hold it, just enough to bring it off idle, and it revs up just short of 1300 rpms. Then the weird shit starts. Without lifting off of the pedal, the etc% drops to 6% and the idle drops as low as 480rpms. It stays this way until either I increase the throttle or completely lift off. If I lift, the throttle slowly returns to normal. If I slightly increase the throttle and hold, the rpms and ETC recover but I have as much as a 200 rpm surge.

Another symptom I have that I'm not sure is linked is the start up doesn't seem quite right either. It doesn't seem to come alive when I hit the key. It sounds very labored. It doesn't start up, rev past idle RPM, and settle back down. It just slowly climbs up to idle rpm. I have tried adding 10% to the start up airflow table with no improvement. Ran out of time to add more.

I have compared the two TBs. The original has the same part number as the new one, however, it is stamped in a different location. There are also another set of numbers that are stamped that are not the same.

Any help is appreciated. I have tried putting my old TB back on. Again, I ran out of time tonight. I have attached my pre-scaled and scaled tune, and logs with the new TB with the scaled and pre-scaled tune.

Sounds like a simple idle airflow issue to me. When you rev it a bit and let off the throttle does it undershoot the commanded idle and then return to it?

No sir, it doesn't. Never goes down below commanded idle after a quick rev(~1400rpm)

Here's what I came up with tonight. I put the old TB back on and with either tune, all was good. A slight throttle increase would nev the engine to 16-1800 rpms and hold.

With the new TB and either tune, I still had the dip in RPM with a slight throttle increase. With either tune and the new TB, it would rev up normal with a quick rev.

I pulled the two numbers that are different off the TBs.
Old TB: 29108F0083
New TB: 25506F0252

Both had the same GM part number: 12570790

Not exactly. When I bring it just off idle, the engine revs up for a second or two and then the ETC% drops to 5-6% and the rpms fall to as low as 480.

Well G8GT, you called it. It was an issue with the final airflow minimum table. Apparently, it didnt appreciate me cutting it in half. I came across a post where I think DSteck and Greg were talking about not scaling the idle tables at all. I figured it was worth a shot. I put the unscaled RAF table in and the issue was gone. It friggin blows my mind. I scaled an 05 GTO's idle tables and it went off without a hitch. Mine apparently, wasnt having any of it.

I never scale idle control. It is separate from the actual fuel delivery side.

This is the first I've read of this. Everything I've ever read about scaling says to scale anything with an airmass value in the table. Obviously, that isn't the rule. Can you venture a guess as to why it worked on the '05?

Couldn't tell you. It's hit or miss.

It's because I'm a badass.

:P

All things aside, I've done it myself, enough times to know what they act like. The oncoming airflow supersedes the ramp up airflow table which causes it to shut the throttle and force the airflow min table to act without modifiers. This causes the idle to dip. If you watch closely the TB will actually close completely and reopen again once airflow values have fallen below the min + airflow ramp up.