What causes it? I'd think it has to be some sort of turbulence in the IM, considering the TiAl I'm using has an 11lb spring in it.

 

It could be alot of things but make sure the vacuum line is routed correctly. It should be directly from the intake manifold to the BOV. Mine once went from the intake to MBC and then to bov which caused a delay in it opening and drove like crap since the vacuum had to travel thru smaller holes, fixed it and drove much better with less flutter and stuttering.

Is the line going directly to the intake? A completely seperate line than with the FPR and all the other stuff that needs vacuum, it should not share vacuum with anything else (for best operation anyway)

 

Yup, dedicated line for the BOV. AMS F1-I intake mani too, if that makes a difference.

 

when you let off or are on the gas?