Hi Jordan,
I have had similar issues with the low idle ... see this thread --->
http://www.sl113.org/forums/index.php?topic=18504.25My post 25 and Dan's reply (Benz Dr,) in post 26
As you can see you need a simple adjustment on the throttle valve and the injector air valve ,,,
As for the heating issue I have it too ... the jury is still out if I need a new clutch fan or not meanwhile I will avoid traffic jams (stop and go traffic) also I purchased some "Water Wetter" today. I don't know if you can find it over there it is a red liquid you add to your radiator. The claim is that it will somehow reduce your water temperature and make the water wetter in your radiator.
I found my water wetter product in a Performance Bike Store. This time of year with high temperatures people use it quite frequently.
Good luck.
PS. If your car is a 280 like mine then it is apparently a common problem (engine high water temperature). The reason for this is that the engine block for the 230, 250 and the 280 are all the same and the cylinder bores for the 280 is larger then the 250 and 280. So consequently the engine block internal wall sections are thinner and therefore more engine heat penetrates or for a better word radiates into the cooling water passages of the engine. There is good background information in the Technical Manual ---> Search Radiator or Cooling and you find it. Don't run your car with the water temperature in the red zone your engine block will warp / distort and or you blow your engine.
EDIT ---> I see you are not a member, since you are not a member yet, I don't think you can access the Technical Manual on this forum (worth it's member fee in Gold BTW) so do join if you plan to keep the car. It has lots of good stuff in there one of the best resources I've seen on any forum.
Anyway, I made a photo for you of the Water Wetter and a similar product Flex-a-Chill ... I'm sure you find something similar that people use over there if you cannot find one of the two in the photo.
Note, when you add it to your radiator first remove about the same amount, do not overfill the radiator. Check your manual the black overfill tank should be about half full when the cooling water is cold.
web sites are;
http://www.redlineoil.com/product.aspx?pid=74&pcid=10or
http://www.flex-a-lite.com/accessories/radiator-accessories.htmlOne more Tip ... I see your car is an Automatic like mine ... If in heavy traffic or long traffic lights I now shift from being in gear to Neutral ... that helps a bit as well.