A shout out for help on a misfire mystery. My 1994 E320 wagon received a major 30,000 mile service recently.....new wires, coils, etc. Within days it started to sporadicly misfire. The engine would start on 4 or 5 cylinders(?), not sure how to tell how many were working, and run quite rough and very rich as I could smell gas quite easily. After taking the engine cover off and manually checking all coils and connections, the misfire went away. I did not find anything loose, but I did shake each coil a little before re-covering. Again, yesterday and today, it started rough with a definite cylinder not firing but after warm-up and a few minutes of driving the misfire disappeared. Throughout this mystery, the check engine light has NOT activated. Any suggestions as to what to look at next to try and solve this bothersome development?

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1994 E420, 1994 E320CE, 1994 E320TE and 1991 300SE