08 Audi pressure loss question
 

I just bought an 08 a4 2.0T (manual).. The car has an aftermarket BOV installed. Occasionally the car lags when accelerating from a stop and then kicks in full throttle, or the RPMs flutter when accelerating in 2nd gear. The other day when it was acting up I could hear the BOV releasing pressure when I was simply coasting to a stop at a light, my RPMs drop, the engine shuts off..

I just replaced the B1S2 oxygen sensor (the other one is fine), the check engine light is not on, and today it just did the same thing traveling up a hill. It would barely sputter forward after being stopped at a light, and then when slowing down at another light RPMs dropped and car stalled..

What I know for a fact is my BOV is releasing pressure at some odd times but it doesn't seem like that can be the sole problem.. Or maybe something else is causing that? Not really tryin to just start changing spark plugs, fuel pump, throttle position sensor, etc. just to see what works.... Any ideas?