Tial designed this blow off valve to work correctly with vehicles that rely on recirculating the blow off valve into the intake system before the turbo to maintain factory-quality drivability.

Many factory turbo setups feed blow off valve discharge air back into the intake after the air flow meter. The factory air flow meter is expecting this air to be there, and sends a signal to the ecu to provide enough fuel from the injectors to provide for it. If you upgrade to a non-recirculating blow off valve that dumps to the atmostphere, the discharge air is no longer feeding back into the intake after the air flow meter. This creates a problem because the ecu, and air flow meter do not know that this air is no longer making it back into the system, but its still assuming it is, so it continues to provide more fuel for the air its not actually getting. This creates a "rich" condition where the air fuel ratio gets unbalanced by having too much fuel and not enough air during "off throttle" conditions like shifting or decelerating. This can cause the car to stall, sputter, and decrease drivabilty in general. Even worse, it can cause spark plugs to become fouled, ruining them .