[MMGT1]

I found in mine, a 3400, as the maf would get dirty fuel trims would go lean. What I have deduced is this: as a MAF gets dirty it looses its ability for heat to be transfered to the incoming air. This is how our MAF works. It keps the sensor at x temp while active. Incoming air cools the wires and the computer is reading, in Hz, what is required to bring the sensor back to temp. This drop in temp and raise in electrical output is how the computer determines the amount of air incoming. Then it is using the IAT sensor to adjust timing for said temp of incoming air. When the sensor becomes dirty, it can no longer read the incoming air as the air can pass over the sensor without properly cooling it causing a lean condition! Your #1 O2 sensor reads the "malfunction" and adds fuel to try and fix it. This goes back and fourth for a while until the PCM learns the God awful trim that it is being tricked into. Bottom line, it will wind up rich when the car "thinks" it's fine causing bad mileage. If anyone has any other thoughts on it go for it!
But I will say this, a MAF out performs a MAP sensor any day of the week. A map cannot make changes as quickly as a MAF, period. Having the MAP properly working is very important for startup and for entering PE mode, but the MAF is where it's at guys!!