Bad boost fluctuations... I'm out of ideas, please help
I have an '02 wrx that is experiencing horrible boost fluctuations and quite a large loss of power. It has about 65k miles on it and is completely stock except for a new bcs. The problem started a month or so ago and has only gotten worse. When I floor it, the car boosts up to about 14psi the drops to 9 or 10 then boosts back up to 14 then drops back down to 9 or 10. It just jumps back and forth, never holding at one pressure and you can definately feel it in the car. I have put in a new bcs, checked all my vacuum lines, and even changed swapped the complete turbo with wastegate for another stock td04 set up. I can also really feel a loss of power now that has gotten progressively worse even with the new turbo, it doesn't pull near like it used to. I am very puzzled as to what is causing the problem and frustrated so please help me out if you have any ideas. Thanks!