I doubt that it's the MAF.
The P1129 applies to only ONE cylinder bank, if the MAF were bad you'd probably have errors on BOTH banks.
P1129: Oxygen Sensing Adaptation Area 2 (Cylinders 4 - 6) - Lean Threshold
so it could as well be a bad O2 sensor (or the obvious: gas cap, oil cap)
here is some good reading:
http://www.renntech.org/forums/index.php?showtopic=7558
I just had a P1128 fixed by replacing the oil filler cap which had a leaky rubber seal and was drawing air ...
How many miles do you have?