You may have over oiled your filter thus throwing the 1151 code - that will foul the MAF sensor with oil and crap and it won't read the air flow enough and thus not add enough fuel giving you the lean code. You can fix that by taking the filter of and shaking the oil off it (a good way to do this is put it in a zip-lock bag and put it in the spin cycle in you washing machine with NO WATER - just don't let mum see do this or you are screwed!)
To clean the sensor, with the MAF off, spray electrical contact cleaner on the wires in the sample tube. Gie it a good dousing, but don't touch it with anything else.
You may be suffering from a short in the O2 harness too, or a porr connection. clean off the prongs in the harnes with a cotton tip and some alcohol, and reconnect, reset computer and try again. I don't think that the sensor itself is bad due to it beeing changed twice already.
