Overboost problem

[Guern]

I have a 1991 s2 2.2T 20V, for a while it has been overboosting and under hard acceleration has been jumping violently. The garage have looked at it many times but can not find what is causing the problem.

Has anyone experienced this problem before?

 

[Doug_RS2]

Boost leak - check www.s2forum.com for lots of threads on how to test and fix.