That's pretty typical for an intake manifold, especially if your EGR is still hooked up. I think if you really want to clean it good, you should take it to a machine shop. You may be able to get away with soaking it in B100 for a night, though not really sure how much additional scrubbing you'd need to do.

I'm going to be pulling my IM off pretty soon too, looking forward to seeing the nastiness inside.

__________________
-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon