I am not certain but I believe the darn thing is called a Thermo Vaccum Valve.
Also I am pasting something from a recent post of mine regarding the Idle Valve breather hoses -
if you need more info about replacing them I could give you more details. ---
"Thanks Peter (psfred) for your help with trying to cure the rough Idle on my 1987 300SE/Euro. I finally got to replace the two breather hoses on the Idle Valve. Gladly I must say that Idling has never been better. There is only a hint of an occational shudder when the car comes to a stop. It is Almost MB perfect.
This was the last chapter, I hope , after replacing fuel pump & filter, plugs ,wires , cap , rotor and clean flushing the Idle valve itself.
Like you said the hoses were a bear to replace , especially the one to the Manifold. I did manage to do it myself though, both from the top and bottom . Had to remove the cold start valve though (reached from above) , in order to fit the hose into position (pushed from below).
In order to reach and replace the second one(going) to the fuel distributor you really need to remove the Idle Valve itself
I was wondering if members here would believe that the changing seasons could have something to do with better Idling as well. It is colder and perhaps the Hoses and fittings and valves do not expand as much..any thoughts on that ?"