I've had my W212 E300 for barely a week with about 120 miles on the odometer so far. I've noticed this issue from the day I took delivery of the car. Basically, while driving at about 70mph or above, the car feels alarmingly unstable. Even with the steering straight ahead, I can feel the car drifting slightly left and right, like there's a constant crosswind or something. An alignment problem would normally feel like it's pulling to one side but the pull would at least be constant. On the other hand, the drifting I experience feels as if the car simply can't keep to a straight line and keeps wandering from one side to another. The steering feels very vague too. I would imagine this happening to a compact Japanese sedan, but certainly not on a Benz. Anyone else noticed the same thing?

 

That's odd. I've had mine about a month, but last night was the first time I was able to get it onto a highway and go over 70mph. I noticed something similar, drifting side to side, constantly having to make adjustments, but I thought it was the wind since it was really windy last night and today.

 

My 2010 E350 4matic had same issue. I think it is tire. Mine did it for about 3000miles, then it gets better. I did check the alignment and wheel balance at around 1500 miles on it. It was all fine. I did test other e-class, it was similar but little better in sport version. Then it is my wife's car, so I did not drove for last few months. Recently, we had ~800 miles trip and I drove above 70 miles. It is way more stable than before. So I guess it is tire.

Back in 2003, I had yokohama installed in previous E-class, and it was moving left and right depends on road. So I returned them and put michelin. Then it was fine.

For current car, I have continential and I think this tire needs break in.
Also from my experience, left-right move is mostly related to tires.

 

Thanks for the feedback guys. I guess I'll just run it in a little longer before rushing off to the dealer.