[Hethj7]

Is your mass air meter calibrated for your 30# injectors?

Also, is your car actually backfiring, or does it just make a popping noise that sounds like it may come from the exhaust? I ask because my car used to "pop" at times. Turns out it was a fuel injector going bad. That could also explain your slightly lean condition.

Not that I would normally recommend going to a dealership, but if you rule out other causes for the problem, Ford can flow test your injectors for an hour's worth of labor. I am not sure how they do it, but when I had it done, I am pretty sure everything stayed in the car. They charged me for an hour of labor and gave me a nice print out of what each injector was flowing. Just a thought.