Good news is that the 73 is a fine car, however not collectable. It was way ahead of its time when it was new. Great independent rear suspension, rear shoulder safety belts, nice size body. Yours being a 73 has the smaller bumpers which is much more attractive than the ugly ones that were added in 74 in North America.
The M110 engine is a wonderful engine, very smooth and powerful.
Bad news is that it has one of the worst carbs ever made (this may be an exaggeration). The Solex 4A1 carb is very tempermental and prone to warpage due mainly to someone over-torquing the 4 mounting nuts and possibly the air cleaner cover.
There are other causes of rough idle that should be checked before blaming the carb however. Check for vacuum leaks, check spark plug connectors, rotor, distibutor cap, coil, do a compression test.
You could have more than one problem as well. Your hesitation could be due to the secondary flaps (the larger ones) on the carb sticking or opening too easily. There is a tension adjustment that has a set screw to lock it - loosens sometimes or someone might have been messing with it. Press the flap down with your finger & check for smoothness and that there is resistance (from a spring). There is a procedure for adjusting it but I don't know if it is in the manual (using a weight and checking the flap displacement).
My first Mercedes was a used 74 280 close to 30 years ago. Learned a lot from doing my own work on that car and it gave me many years or enjoyment.