is there a lot of dust (fuzzy)or just a few specks? if there are only a few, knock them out with 600 grit, and go ahead with your topcoat... thats what primer is for, finding imperfections. IF it is to the point that it looks fuzzy, cut it down with 320, and reprime.... you could open all the windows in the car, and blow the interior out with compressed air, it might keep you from having the same problem a second time.