1998 C230, can a coil be going bad without throwing a code?
 

When I had a coil go bad it failed completely (on one side) and I got a code. Now I have "sometimes" a slight hesitation on acceleration. Trying to come up with some theory to explain it.

I doubt it. Any misfire caused by combustion misfire are stored by ECU.

Have you cleaned (special solvent) OR replaced mass air flow sensor?

Yes. I replaced it about 6 months ago with the correct Bosch PN. It worked fine after that, until recently. It seems to only do it after it warms up but I can't say that for sure. It doesn't do it consistently, but when it does, it is very noticeable, and very bad when the AC is on.