On these early to mid 90's m120's with distributor caps. The combustion is critical, and the two cheap sensors responsible for this are those four-wire temperature sensors on the thermostat pipe. It is the same sensor on a M119 as it only has one..

Change both, and I think you will solve your problem providing your MAF wiring is good.

Ohh by the way MB Star will say it is the MAF sensors which is dead wrong. I'm old school, and you do not need star for these distributor engines...

Martin