Hi

I had the same problem only the other way - mine had way too much boost. Mine was related to the good ol' amal valve (the crappy plastic thing on the front of the intercooler).

Lets assume that you are not running the standard chip - which is important. If not, then you will probably need to modify the amal valve input pipe diameter to restrict/ release pressure to achieve your target boost.

It is possible to completely bypass the amal valve (which I have done) and replace with a variable pressure valve. This is not without risks, and if not properly set up will lead to major problems, and I mean major problems.

Suggest that you speak to local tuner to help you resolve the problem.

hope this helps

JJ