I'm still learning about how best to detail porcelain coated grill components, but automotive paint cleaning products work well on painted surfaces, and they can hinder the growth of rust too.
As for using these products on porcelain, I don't recall seeing any negative effects on my stuff (including charcoal grills), but as Jon mentioned above, 0000 steel wool and Simple Green should remove any above-surface defects. I have even used 0000 steel wool and Dupont's #7 compound on car glass to remove acid rain stains with good results. (spot test first though)