The fuel trims, shown on the scanner, are what the ECU is thinking the mixture is. If it's thinking rich, then a signal is telling it that the mixture is too rich which would point to the MAF. I know you changed that, but it is a common culprit with no codes. Maybe you could swap the old one back in to see if there's any change at all.
Clogged injectors? Possibly, but it sounds very rare.

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