I've been working on the boost PID of this particular big turbo B6 A4 for entirely too long.

There's a certain point around 5,200 rpms where the boost jumps and plateaus for a few hundred rpm, and then settles back down.  This particular spot in the rev range poses problems when especially when coming into boost during that range.  Boost goes crazy and oscillates all the way to the end of the pull.

The first two attached screenshots show the boost profile with the entire KFLDRL table reduced by a third.  Yes, boost does not follow requested in this log, it was one of the earlier versions to get an understanding where the steady state would be.  But what it does illustrate is even with an averagely linear duty cycle, there's this big dip, spike and plateau around the same RPM range in just about every pull.  I've been fighting this area by attempting to modify KFLDRL to account for it, but my efforts have failed so far.

The last screen shot is the closest I have gotten the pid to being stable, but I can never seem to account for whatever is going on at 5,200rpms.

Turbo in question is a GT2871R, internal wastegate with a T25 manifold and custom manifold to turbo spacer.

Would appreciate any pointers.

you da man DD.  Incoming.