Thanks for your advice. I live in England and the C180 is a 1.8 litre Mercedes saloon. Apparently these are not available in the States...probably because they are at the lower end of the model range.
Returning to the problem, I took the car in for a diagnostic at the local dealer which indicated a faulty actuator. At great expense and because of time pressure I am also having to have the car repaired by the dealer. This is against my normal practice and makes me appreciate my other car, a 1984 VW, which is not equipped with sophisticated electronic controls and as such has been amenable to my repair over 215k miles.
Once again thanks for you replies.