I've done this in the past and maybe the closed loop helped ?, but I'm really starting to wonder if the ecu is ignoring the MAF, but not setting a check engine light for it. The adjustments to the MAF transfer function usually seemed to do something, but nothing you really expect, and it was in closed loop at those times. Now that it is off I'm not really seeing any change. My guess would be the car is ignoring the MAF because it thinks it's data incorrect , or the minimum pulse width for the injectors is keeping the car to rich at low throttle and idle. I tend to blame the tune going down the tubes on the change to return fuel, but I'm not positive I ran the 80# injectors return less.