Oven cleaner will EAT! aluminum! bad idea!, some carb cleaner and a brush will knock it out, I threw mine in the parts washer at work for a whole day, slapped some HPNK on it, it's purdy now!
You can get more power out of ANY engine!!!
ASE Master certified engine machinist, gas and diesel
Sounds like it was left on too long. Wet with warm water, shake off water, spray item with oven cleaner, soak no more than 5 min. Wash it with water, repeat if necessary, Always flush with large amounts of soap and water. This will remove clear coat, anodizing and yes it will even lightly etch the surface of aluminum. Parts will need polished with your favorite polish after wards if you leave it on longer it will keep eating away, Lots of things are cleaned with mild acids, but we don,t soak them and go away.......................Drop a nail in a bottle of coke and look at it a couple of weeks later.
I have cleaned 3 intake manifolds and a couple of truly filthy AMC bell housings this way with zero problems, I would only do this outside.
John
i had a similar situation after driving around with a cracked exhaust manifold for several months. i surmised that the crack upstream of the O2 sensor caused the ecm to detect a lean condition and was dumping in more fuel to correct it. my fuel mileage was suggesting this as well. when i took off the intake i was horrified to find thick, scaly, black, sludgy gunk. i scraped out what i could with a flat screwdriver and doused the remainder with brake cleaner and it wiped right off. hopefully your "assistant" doesn't accidentally hand you white grease as mine did. the first spray came out and i thought, "geez i don't remember it foaming like that. and it's not really evaporating at all..."
in his defense, both cans were similar in color and i did place them side by side on the shelf.