Temps over 90C are by no means considered overheating by Mercedes standards. The fan clutch does not kick in until the engine starts to see 100C anyway. Aux cooling fans do not kick in on high until 110C and cycle on and off of low speed with the A/C on according to refrigerant pressure.
Exactly how hot does the engine get at idle? These cars are designed to approach 100C even with everything functioning properly at idle. On a very hot day at idle with very high A/C load, engine temps around 110C would not be considered that abnormal. If it gets any hotter than this, then there is a problem.