I don't think it's MAF, not yet anyway. I my experience with E320 and SL500 when MAF needs attention there would be fuel trim fault codes and possibly misfire code in addition. Do you have any issues under load? Like 40 mph and put accelerator to the floor… any hesitation, stifling?

If the issues are only experienced at idle I would start looking at possible vacuum/ air leaks. Visual inspection first to see if there is something obvious. If not then smoke test.