Harness always possible,but you may have a bad coil.Put in some new plugs,inspect the old one's for fouling.My car had a miss but with new plugs ran fine for a few weeks.then I replaced the #6 plug and ran fine again.Changed the coil on that cylinder and its fixed.I replaced #6 because that was the plug that showed any wear after 2 weeks.
Some what possible MAS SENSOR,but not sure if mercedes runs ok with it unpugged.Most cars with bad MAS sensors run very well with that sensor unplugged.Quick way to check mas .
Plug wire's and coil extensions need to be checked also
Good Luck
Rich

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88 300E White, sold 9-04
88 190E Black 2.3 sold
90 300CE White, Grey sold 12-24-04
92 400E White,Grey Sold 5-06
90 300CE 91K Signal Red,Black Sold 2007
1989 300CE Smoke silver,Tan Sold 1-08
1993 300E 3.2 M104 motor
1991 300CE White,Grey
1994 E420 beautiful car,gone to new home
1994 E320 Smoke an Parchment.Beautiful car