Unless there is a large crack in the piping? and only when the vacuum starts does it open? Causing it to stall? Piping all new?

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1997 White GC8 WRX - 3" TBE, Apexi pod, V6 STI TMIC, Kei Office coilovers, Whiteline F strut brace, GReddy Profec B Spec II, 2004 F&R brakes..