Not sure if you have these tables or not. I saw one file were the combustion pressure limit was restricting spark towards idle. It was near the edge of a load point so as the load changed slightly at idle it was causing idle spark to jump around. Side note, after seeing that I used those tables to lock my spark down at idle. (Making my idle spark advance, limit, and minimum all the same) Adjusting my predictive and effective throttle tables helped stabilize my idle (not 100 percent perfect but a ton better) Also was able to adjust idle areas of MAF better since timing wasn't jumping plus or minus 10 degrees and was staying stable.
Don't know if any of this will help but figured I'd share.
idle spark pictures.PNG