E21 carburetor 315 engine stalling, rough idle - HELP

I have low mileage (45000km) e21 315 carburetor (Pierburg 1B) engine in my

I start my engine. Cold or warm - no problem, starts OK. Rpm goes up to ~1500 and all is well. Then, as engine warms up, and needle on temperature gage goes just outside blue part, when I stop at traffic light - it stalls.

When the engine warms up more, it does not stall anymore. But idle is rough (I could not feel it running before this problem, now I can feel vibrations on my steering wheel).

I read somewhere that the way to check vacuum advance on distributor you rev engine to ~2500 rpm with vacuum hose disconnected, then connect it, and you should notice a difference. I can not notice anything. How big difference should it be?

Also I noticed temperature switch (next to temperature sender for temp gage that I ordered to replace (needle on temp gage jerks left and right sometimes). This switch seems to be open until 35 deg Celsius, then close (did not check, but I will). What is it's function (I do not have fuel injection, only carburetor).

E21 carburetor 315 engine stalling, rough idle - HELP