I bought the car as a Mercedes-Benz CPO car with 60K miles in 2006. It has always been serviced according (and mostly exceeding) to M-B schedule including fluids, spark plugs, brake flushes, etc. It has never had a problem like this and most replacement items failed after a long service life.

The vibration is recent and happened over a short period.

Today I pulled all the spark plug wires and measured the resistance. I found one at 2830 ohms. I changed that one and three others that exceeded more than 10% tolerance; i.e. any with readings more than 2200 ohms. No real difference.

I FEELS like a miss, but without any codes it makes me scratch my head. And the car runs strong and is very smooth just off idle.