You said you did the sensor on the back of the fuel rail. The one on the back of the fuel rail can not be changed it is set at the factory and the book says to change the whole rail if that is a problem. Mercedes does not change them at the dealerships just the rail. If you removed that sensor. I am willing to bet you got it in there good enough for it to run without an error code but not as good as the factory settings. It is adjustable maybe before you buy a new one for $325 you should micro adjust it. I think you should mark the rail in both directions and mount a pointer on the sensor. Adjust it left one notch and then test it. Adjust it right one notch. Until it runs really good. If it starts to throw code you know you did it wrong.

Good Luck with that.