All signs point to fuel delivery. Not likely mass airflow meter.
How many miles?
If the fuel filter is several years old, I would replace that as routine maintenance.
Sounds like it is cold where you are, so put in a bottle of Heet to absorb any water you may have in the tank.
After that, it is time to check fuel delivery pressure and volume. You may need a fuel pump.
Mid-grade is OK in a '93. e36s are very tolerant of different fuel grades. e46s are not so forgiving.