Larry .. re carbonization

I'm in the process of changing out my glow plugs
in my 1996 E300D ( ~90,000 miles ) which on this
model requires the removal of the intake manifold ..
and guess what ?? Gobs of black goo as you just
described .. This stuff is a real mess .. I could
try and vacuum some of it up .. I don't want to have
any 'break off' and get into the engine itself ..
Do you know of any solvents that will suspend this stuff
without hurting the metal ?? I don't see how the "Italian
Tune-up" could solve this issue .. BTW what's the source
of this 'goo' in the first place ??

Jim in Ct ..