Somewhere in the forum is information on how to build a code reader for the W124 using about $10 of radio shack parts.
Back in the day when I was troubleshooting my '95, everyone was recommending coils, plug wires & I don't know what else. It took a long time (days/weeks) before the car finally threw a MAF code. The car was driveable at speed, however; it was worst at idle.
There is a sub-forum for good indy shops if you need to throw in the towel, and one recommendation your area was:
Euro Care
1011 State St # B
Lemoyne, PA 17043
(717) 737-6776

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Prost!