The rough idle and surging is normally the "idle control valve" I talked to a mechanic and he said to remove it, clean it out with carb cleaner, then spray inside with penetrating oil.
To get to the idle control valve, remove the air cleaner. You will see a cylinder about 4 inches long? It is shaped like a "T". It is in a rubber mount that is help by 2, 10mm bolts. On the front of it are two wires that join into 1 socket on the valve. It has one hose going off each side of the "T". Hose on the right goes to the fuel distributor, I believe. I am not sure where the one on the left goes. It is hard to see where it goes to. Once it is out of the car, spray the inside of the valve with carb cleaner and then try to get out all the excess out, maybe after it has set for a minute or so? Then spray with penetrating lube and reattach.
I know I am kind of rambling but the surge is common on 300E's and this is how I partially fixed my fathers. I also tried to be really simple as to the fact that I do not know about any mechanical background which you may have.
I am sure though that this will help or solve your problem.
David