I have 300CE Coup. Mercedec Car Model 1993,
When I first Start the car (after it has been stopped for more than 10 Minutes), the RPM goes up nearly to 1250 then fastly goes down too much, after that the car start shaking, then the RPM goes to stable state (Normal)

could be air leak around manifold/intake,or poor engine coolant temp sensor and wiring to it.have you had emissions tested?

Possible as written above, Hoever I would more so suspect (by your description of indications) that you have an inherent malfunctionthat is relativly comon being the purge valve needing removal and replacement. The part is about 72 dollars and after proper diagnosis should not total more than a 2-300 dollar final bill at a Mercedes-Benz Dealership Mercedes-Benz vehicles made after 1999 no longer carry this inherent trait as the purge valve design was finally revised; putting a lengthy history of their vehicles being prone to this malfunction to an end.