High Water Temperature While Idling

I come from a tropical country(Singapore) Recently, I've noticed an increase of the average water temperature of my car(higher than usual 88-99 degrees C). Fearing for the worst, I changed the radiator, thermostat and coolant. The situation got better after changing.(85-87 degrees C while car is in motion) But when the car is not moving(e.g stationary at a traffice light junction) the water temperature increases to around 97 degrees C. After which it will take quite a while (around 3-4 minutes) before the temperature starts to drop. It seems that the cooling system is not as responsive as before. I've checked the engine fan, auxilliary fan and fan belt as well, they are all working. What could be causing this???

Car:MB E200 W124
Yr: 1994

Repair History:
Heater Control Valve was not working.Hot air came out of the 2 outer a/c consoles in the passenger cabin. Went to MB Service Centre. Technician told me that they will block the passage of hot air flow into the passenger console.(Because it is more expensive to replace the heater valve)(Heater control valve not replaced)

Catalytic Converter changed due to noise coming from exhaust during sudden acceleration.