here is a procedure if you wana try it, it works wonders on rust. but..... you will have to test it on aluminum...
take a large garbage can, fill with water enough to cover the part, then add "borax" laundry soap to the water just to the point where no more can be disolved in the water anymore. you do not want solids (powder) floating in water.
then get a metal rod, place metal rod in side of tank and solution you made, stainless steel works good, or just a piece of straight clean metal. DO NOT LET THIS ROD TOUCH THE PART YOU ARE TRYING TO CLEAN....!!!!!
then take a very large battery charger that stays on all the time. i think a min 40 amps is good but see what yours does, hook positive to rod on side, and neg to the part you car cleaning. turn on battery charger and observe. Depending on the amps you are using you will see bubbles come to surface, those are hydrogen gas, so do not do this in a garage unless you dont like your house. ha ha
after a short while you will see paint, rust, and other non metal parts come to surface and come off the part you are cleaning.
NOW I SAY AGAIN METALS ARE DIFFERENT, ALUMINUM WILL NEED MORE SUPERVISION THAN SAY A CAST IRON INTAKE!!!!
this works good and I have done this many times, but the waste is troublesome as you change the water/soap into something not desirable for well anything when you are done.
good luck
just take it to a machine shop and have it hot tanked..