I can't speak with the confidence of a service agent, but
If it's not showing knock retard even though it's pulling wads of fuel out, then I'd imagine it's actually running rich
Faulty O2 sensor returning out of spec measurements could have it thinking it's too rich, having ECU attempt usual corrections but throw CEL when it can't be brought into line.
Likewise a MAF sensor fault could have it actually running rich if it's reporting a higher airflow than actual.
So...O2 returning measurements indicating it's richer than actual
Or MAF returning measurements indicating higher airflow than actual.
I think the spark plugs are a red herring in terms of the CEL. Definately that will have gotted rid of the cold stutters, but wouldn't be resulting in too rich CEL
If it's got a cobb tune on it that tune might be inappropriate for you MAF housing. Is it an OEM airbox and MAF housing?
If it's an OEM airbox and unknown tune I would immediately put a stock tune on it. Without the AP on hand I think that's a trip to Mazda, OR flash to Cobb's default mazda OEM tune with a replacement AP.
I'm imagining previous owner parting out mods (such as an aftermarket intake and MAF housing) - removing the mods but not having the AP to return it to stock tune. That might account for MAF calibration being wrong.
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