What year is the car? I think the 102 engine came to Europe in 1980 or so, and that they all have CIS-E (no warm-up regulator, but EHA) It is the same engine as in the 190E 2.3
There can be many reasons for the car to act like this. Bad injectors, clogged fuel filter or worn fuel pump can give symptoms like you describe, as well as bad ignition parts. It could also be the cold start valve, but it's only functioning when the engine is cold, not at 60°C. Another posibility is that the auxillary air valve does not open when the engine is cold, and therefore no high idle.
Let us know if you find out, I'm still having similar problems with my car!