Need Help Deciphering OBDII Codes

[rba]

I have a 2001 3.0L that the Check Engine light is coming on. I pulled the codes, but i need some help understanding what it is telling me.

The codes are:
P0171- System too lean (bank1)
P0174- System too lean (bank2)
P1083 - Fuel System too Rich
P1085 - Fuel System too Rich

Now I know that P0171 and P0174 together usually mean an air leak after the mass air flow sensor...or a bad mass air flow sensor. I replaced the mass air flow sensor....granted it was used...but the same codes are showing up. Maybe I got a bad replacement?

What is puzzling to me is I get the codes that says its too lean..and at the same time codes saying its too rich! It seems like there is a paradox here...too lean and too rich at the same time. maybe I am not intrepting this right.

Can anyone help with the "too rich" codes. i dont fully understand this.

Thanks.