I am glad that your problem is solved. I have a 300SEL 89 and I have a rough idle meaning that the car will idle at right rpm but the needle fluctuates a bit maybe 25-40 rpm. It does not do this all the time. Other wise ths car is fine. This rough idle is an annoyance. Some one told me that the mixture control unit could be bad.
Could you attribute your problem similar to mine and will a fix like yours be the solution.
Thanks for the reply