The Mitsubishi Evolution is a sensitive car primarily due to it's Karman Vortex MAF. This sensor makes it very sensitive to any turbulence, delay or reverse flow in the turbo inlet air stream.
The number one mistake that tuners/users make with our DV/BOV products is related to the vacuum signalling/control of the product. If you're using a manual boost controller, or external solenoid to control boost, make sure that it does not share a line with the DV/BOV. What this does effectively, is bleed the boost pressure used to close the DV/BOV under boost. It will then work to open the DV/BOV under boost. With most Manual Boost Controllers (MBC) there exists a bleed hole in the device. If you are using the MBC with a post-throttle vacuum source, you are creating an always-on vacuum leak past the MAF, that is made even worse under boost. When it comes to controlling the DV/BOV opening ability, this bleed takes away vacuum force from opening the DV/BOV. This delay in opening is what results in bucking and bad air flow timing for the MAF.