Hello,
With a MAF car it's best to run a closed loop "sneeze valve". Unlike ATRs, which is good, this style dicharges the metered air back into the turbo and engine which reduces surge on the turbo. It also, as mentioned by others, eliminates the off throttle bog and stall. Explaination available upon request. We offer an inexpensive kit for about $100 that works great.
Hope this helps,
John @ ESP Products