Please help ID this part
 

This is for a 1975 450SL

I think it's part of the vacuum system but would like to know for certain and also what its name is and what it does.

It's the silver, circular object with two pink rubber hoses leading from it. It's on the left side of the engine and the pic was show while standing on the left side of the engine compartment.

Reason I ask, is that I found the lower one of the two pink hoses disconnected after this morning's drive when I had noticed the idle being very smooth as opposed to the usual rough idling. I tried running the engine with it disconnected and connected and did not notice any perceivable effect while the engine ran. So am curious as to the purpose of this device.

It's your EGR Valve.
(Exhaust Gas Recirculation)
It's part of your emission system.

thanks very much
 

now that I know what it is and what it does....will see why running with the lower hose disconnected appears to have no effect.