what ecu are you using, I'm wondering if that matters at all? a6 block? That is that old ass teg? 1.6L ? DO you have an idle adjustment screw? Maybe it needs to breathe a little more, and it is leaning out, until the O2 sensor reads it and corrects it?

I dunno, grasping at straws, best of luck, let us know, anyone else have ideas?

-PHiZ