I searched all around and I cant find anything on the exact problem that I am having. I put a turbo xs standard boost controller on my car the other day and I cant get any less than 12 psi. I thought that maybe it was my wastegate because the diaphram had a small hole in it so I got a new diaphram. Last night I installed the new diaphram, put the boost controller back on and I am still having the same problem. I have checked to make sure that the boost controller is not hooked up backwards.
I cant understand why it will hold 7 psi all day long, but as soon as I put the boost controller on it wont do any less than 12-13 psi.

What is the lowest setting on the boost controller? Is it designed for a higher boost level than what you're trying to do? I really don't know much about it but that would be my guess.

mbc only let you boost more. if you open it up all the way it will be as close to what your wastegate is set at as possible.