check everyting around it to make sure no lines are off or worn.Most likely the valve is good the metal tube is partially plugged.Clean it,and old speedo cable in a drill works.
Unit is located under the intake tube going back to the rear of the engine on the pass side
I don't know if the diy was posted in the diy section of benzworld.org if not a search of posts with egr will locate it.You cant miss the tube it is bright silver and goes from the egr valve to the rear center of the engine.
ohlord

 

clogged EGR can cause alot of issues such as rough idle and what not but what i see happen alot on the EGR is the solenoid valve stops working-how this works is the solenoid has engine vacuum running to it-when EGR needs to be open the ECM then sends a signal (power) to the EGR solenoid in which the solenoid opens and allows engine vacuum to open the EGR diaphragm and allow exhaust gas to recirculate-most of the time the solenoids fail which will not open the valve-not saying it couldnt be clogged just tellng you what i see alot of

 

I haven't pulled the EGR valve or tube yet, as I found the size of the nut on the tube into the valve was larger than the crow-foot wrenches I have. My largest is 22mm which is a "no-go" fit. Does MB call for a special tool for this or will a 24mm or 15/16" crow foot wrench do the trick?I find I can mess up more without the right tools than paying the price for the right tools. Myplan was to get access to the tube, clean it out per ohlord with a drill and wire auger, clean up the valve with MAF cleaner, and reconnect to see if that takes care of the error code. Other suggestions???
Thanks for the information.