Makes me wonder how much dust might be on the MAP sensor wires (affecting it's readings), and how much dust has already gone into the engine. Has to be coming from somewhere . . .Yes there was dust in box but its not that sealed or anything in front. I checked box was closed properly so dust still coming through then.
Are you sure the air filter is the right one for the car, and is fitting properly in the air filter box parts? Is it a Subaru filter?