Help with light load bucking/jerking.

[SydneyACE]

I have a bucking/jerking issue at light throttle, low load cruise conditions (almost as if the car thinks I'm making throttle transitions.)
Initially thought it was A/F ratio related, but looks like it might be timing... not sure.
The graph for my timing looks like a saw blade when it's doing it, so that's why I'm leaning that way. (Not sure if fluctuating timing is CAUSING the issue or adjusting in an attempt to compensate.)
Not sure why timing is changing in a steady-state cruise like that.
Hopefully you guys know where I need to look, or if there's another parameter I should be logging.

2001 Corvette
Manual Trans
LS3 Swapped
BTR Supercharger Cam (medium size)
Vortech T-Trim
LS9 Map Sensor
3 Bar SD OS conversion
Long Tube Headers (with factory O2 sensors and a wideband in bank 1)
80lb injectors

[Pekka_Perkeles]

Start with tuning Base Running Airflow (under Idle/Airflow). Log desired idle airfllow, as well as LTIT and STIT.

[Pekka_Perkeles]

Oh, and your max rotation with ETC seems to be fine now..

[SydneyACE]

Start with tuning Base Running Airflow (under Idle/Airflow). Log desired idle airfllow, as well as LTIT and STIT.

Can you give me a quick explanation on how to do that? Are LTIT and STIT long term idle trim and short term idle trim?

Nevermind, I just watched a video explaining it.

[SydneyACE]

Oh, and your max rotation with ETC seems to be fine now..

I'm still getting an occasional P1515 or P1516 from time to time. Either when I hit the rev limiter or when I'm at very low MAP and low RPM (foot off the gas, coasting down a steep hill, in high gear).

These aren't super pressing issues right now because I know how to keep from getting it into those conditions. (I set the rev limiter higher than I need to shift at.)
It IS super frustrating when it does go REP though because it goes super lean and messes up any of my data-logging that I'm currently working on.
Thanks for all your help so far!

[SydneyACE]

So just an update on this...

I found a solution in a reply to a different thread. Long story short, the difference between my Idle Spark Advance table and my Main Spark Advance table (in the cruising ranges) was too dramatic. The car was transitioning between the two tables and timing was jumping. I had no idea it was still using the "Idle" table at that RPM range.

I just copied my Main Spark Advance table and pasted it into the Idle Spark Advance table, and it alleviated my jerking/bucking issue SIGNIFICANTLY!
It will still buck once or twice transitioning from off to on throttle, but they are minor (comparable to stock) and it dissipates quickly (whereas before it would get worse and worse until I pushed the clutch in).

I had no idea that it was using the "Idle" Spark Advance in that RPM range, but apparently it was. (Which explains why that table covers up to like 4,800RPM.) Not sure who considers that "Idling" but...

[Pistolpetep250]

Thanks for the update. Good info.