E500 is at MB dealer today Symptoms - difficult cold start. When starts, emits a rotten eggs odor and displays an intermittant rough idle. Dealer replaced plugs, caps and rotors on first try last week because advise a 56 code. I delivered it yesterday and they asked to keep it overnight to get DTC on a cold start.

My non coded nose tells me to replace the O2 sensor near the cats. What say you all?

TIA

Tom