W209 Outside Temperature reads high in traffic

[Wingco]

The outside temperature guage on my W209 consistantly reads high when I'm stopped in traffic or when the car is just stopped and idling (read over 30 the other day). This has been an ungoing problem as the only time the indication is reliable is when I'm doing steady road speeds. Have read an old post here in the forums about the sensor being incorrectly located but according to my local dealer that's not the problem!! I am unable to crawl under the car myself (75 and just had a triple heart byepass) so I am unable to verify the sensor position. Now this stuff is not rocket science yet after at least four attempts over several weeks they have failed to solve the problem, despite putting their "top man" on it and assuring me that they have fixed it. At one point they had the car for four days and their so called "top man" drove the car back and forward to work to check that it had been fixed, it had'nt! To my knowledge the sensor itself has been replaced and according to the mechanic (don't think he deserves the tiitle technician) it's all OK yet a two minute test with the car parked and idling would have shown otherwise. I'm about to write to the dealer pricipal (Mercedes Benz Carlisle ) but has anyone else experienced this problem and know the cure. Or would you like to fire up your C209 and see if the outside temperature guage climbs when it's idling
I should also mention that the car was covered by a Tier 1 Mercedes Benz Warranty (I bough it 2nd hand through an MB dealership down south).