I had a similar problem with my '87 300E with 130K miles. Baffles my indie for weeks. I mentioned it to my step son and he had the same problem on his Passat. He changed the COIL and the problem stopped. I did the same thing on the Benz. The problem went away. It is now a recommendaion of my indie that they change out the coils over 125K.
Anziani

'87 300E 175K
'95 E420 Sp. Edition. 101K