I think I may have a boost or intake leak. This problem started about a month after I bought the car. It's kind of hesitant around 3-4k rpms. It emits a light whoosh sound from the passenger side of the engine bay when starting to build boost (no it's not just the turbo building boost, the car didn't do that when I bought it). Also, it won't hold boost (spikes around 13.9 psi then goes to 8-10 psi). My AFR seem normal, 14.4-14.7 when cruising, 11.3 when WOT. It's a 2002 WRX, fewer than 60k miles, besides the stage 1 tune with a Cobb accessport it is stock, one previous owner. Here is what the sound compares to:
YouTube - ‪2002 Subaru WRX. Possible Boost Leak?‬‏
Also, about a month and a half ago, I threw a P0442 cel. It went away a few days later by itself. The cel came back again about two weeks ago, I cleared it, and it hasn't come back. I don't know if this cel is related but any help or troubleshooting would help.
P.S. - I have searched for this problem on this site but all of the sounds and symptoms I have found seem to be different than mine. Thanks!!!