Ok heres what the codes mean..

P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P0170 Fuel Trim Malfunction (Bank 1)
P0173 Fuel Trim Malfunction (Bank 2)

I guess the question is why is there no difference in fuel economy or performance? Also, why the intermittent on for a day, off for a week, on for a few days, etc...? Any help would be appreciated. Should I have posted this in the "Tech Help" section?