Okay i got myself a early 2000 manifold, and started porting it last night with a dremel. I used rags to keep plastic out of the manifold itself, but since this is a used part, it's pretty oily and dirty in there.
1. should i bother trying to clean the inside?
2. if i should clean it, what should i use?
i cleaned the outside of it before porting, and got a bunch of **** of, but i cannot get to the inside.
Since the intake is nothing more than plastic I would just get some foaming engine cleaner / degreaser and fill the intake, let it soak, then rinse it out with a water hose. This should clean it and most engine cleaners are safe for plastic engine components. Someone already mentioned brake clean spray and that stuff really works well and dries fast, but if you elect to use that make sure it's the kind that's safe for plastic, some of them will eat into plastic and etch it or creat soft areas. The soft spots will harden again, but if it etches it that will remain.
I bought carb cleaner (safer for plastic than brake cleaner), and simple green.
Since the simple green is supposed to be safer, i tried that first.... didn't really do much... maybe i didn't leave it in there long enough.
Then i sprayed the carb cleaner in. I dumped it out, and the fluid came out brown / black. Very quick, very easy. Sprayed a shot into each runner for a couple seconds, and then into the TB location... swirled it around... dumped it out... until it ran (mostly) clean.
So, i guess, i'd have to say, if you need to clean your intake manifold, i'd go with carb cleaner.