I posted a reply a few weeks ago about this. I think it was "ASR 400E"? MB dealers have some old bulletins about this problem. The actuator could be the problem, but there's also an updated E-Gas module. The "bumpy road" situation could also indicate a faulty CTP switch. It's a small and inexpensive switch located on the gas pedal. Make sure you get a thorough diagnosis before you spend big bucks on somebody's guess!