on my 190e2.6, the engine began sputtering for no apparent reason and at unpredictable times, when the weather was cold. This was so difficult to diagnose that I left the car at the MB service center. They were able to reproduce the problem, which they traced to a faulty/malfunctioning O2 sensor. This, without the "Check Engine" light coming on, and well below the 60k interval since the time it was last replaced.

Replacing the O2 sensor fixed the problem. The issue here is that the sputtering engine problem can be a safety issue, because it happens with no warning. It almost left me stranded in the middle of an intersection in the lane of oncoming traffic, as I was making a left turn. I had to nurse the car to a safer location until it recovered.

This sputtering engine problem happened again years and many kilometers later, again, without the "Check Engine" lamp coming on. I immediately asked my MB service advisor to have the O2 sensor replaced. They placed a note on the service sheet that it was done at the request of the customer.