did you ever diagnose the problem? I'm having an overboost issue on my
Grand Prix, boosts up to past 20 psi when I open the cutout, I'm thinking
the wastegate can't flow enough gas around the turbo and causing it. May be
the issue with yours as well?
Audi S2 crazy overboost (Audi S2 over boost.)
audi S2 overboost 1,6.mp4
Eprom ultimot audi S2 stage 1: 1,6Kgf overboost with 1,1Kgf final pressure.