I have this strange boost problem... 1st gear = 0 boost 2nd = 5 PSI 3 = 10 but it runs like crap until the boost hits. On one run this afternoon 1st gear produced boost but was very short lived. And sometimes the BOV will pop like it's supposed to and other times it will flutter. You can hear it pop open and close really fast. The car is an S5, it's been regrounded, has new TPS, in process of simplifying the vac rack, FCD, Walbro pump. Any ideas? I'm kinda lost as what may be causing it. Thanks in advance.

 

Seems like maybe the waste gate is stuck open.