S600 1996 73,000kms

Cold Start
1. When I start the car (cold start) the engine idles smoothly and no ASR light.
2. After driving in the heat (in Saudi Arabia) the Car heats to 110c (approx).
3. Idle becomes rough
4. Shift is not smooth (jerky)
5. and ASR light may come on when driving goes into LH mode.

Hot Start
1. When I start the car after driving and the car is still hot (over 100c).
2. ASR light is off at start
3. Idle is rough
4. ASR light come on when accelerator is depressed car goes into LH mode.

Questions:
1.) Any idea of the likely cause(s) I can suggest at the shop with replacing the ETA as a last and expensive resort (shops here will start with the most expensive solution and work back).
2.) Will an ASR Defeat Switch work (where can I get one??)?
3.) Is that heat (110c) extreme or related to the power problem?

Any help would be greatly appreciated!

Cheers!

Daniel