Not sure if this is the answer or if you have already thought of this. This could be because the BOV you are using vents to atmosphere rather than recirculating. The 370 uses a maf so it could be messing up your readings causing you to run rich. Back when I had my turbo honda, I never had this issue cause we used a MAP sensor rather than a MAF. Here is a link for reference.
Can someone explain, Recirculating BOV to me please? | DSMtuners