So I have a 2003 wrx with full turboback exhaust and a turbo xs boost controller and am usually able to hit and hold 15 psi with WOT. Today while driving my boost will peak at 15 then immedietly drop to 10 and back up to 15 then back to 10. Is this just a boost leak or something else. Any ideas?

 

Bad gas, pulling timing, maybe boost leak....