u/Axxdn

I have my 2010 mazdaspeed3 with a motor from a 2008 speed. The car has a front mount intercooler cst4 turbo and recently the car started with an issue 3 months ago where the act. Hpfp press wasn’t matching with the designated press and would lose pressure dropping to 500-700 psi when full throttling. Now the car idle rpms fluctuate up and down and randomly wants to stall, and a strange hissing sound coming from the engine. Car also gives codes P0300, P0171, P0507. Could it be the PRV valve? Or a vacuum leak?