The fan engagement threshold is set high in those cars. I have a 96 myself and it gets above 220 before the fans kick in. I would by a programmer for the car such as hypertech to set the fan engagement to a lower level. Or a cheaper solution would be to hook up a toggle switch for the fans to come on when you need them. This is all assuming your fans work at all. Next time it heats up, turn on your AC. If the temp falls, your fans are in working order :).
I would start by changing the thermostat. They go out, often, or have a tenacy to stick, and are cheap.
Sounds like you need a radiator coolant flush or you need a bigger radiator for your vehicular transport thingy.
To fix high idle problem on a 1996 VS Commodore, first locate the idle air control valve. Unscrew and unplug electrical connector running to the valve. Turn the valve over and clean the sensor for debris.
Is the car filled up with antifreeze? Had the same problem, turns out there wasn't enough antifreeze in the system.
put on ac in car and over heats
Take the thermostat out, start the car and let it idle, see if it over heats. With the thermostat out of your car, it should just constantly circulate water, making it take longer to heat up. If it heats up fast then chances are that your pump is out. DO NOT LET THE CAR REDLINE.
heater core leaking
Check your fan to see if it is turning good with force when hot, you may need to replace the clutch fan.
Water pump Cooling fans not coming on Radiator dirty or plugged
If it only over heats at idle it is a bad fan clutch. If not its the typical Mercedes overheat. Try this link: http://www.dieselgiant.com/thermostatreplacementandmodif.htm
May be your IAC valve (idle air control) they get dirty inside and make your idle act up. Back of the engine toward the passenger side, two bolts and hard to get at.
Bad Head Gasket. Common problem that happens on almost all Legends between 120K and 180K. I just had mine replaced.