At any speed, once the cruise control is activated it starts surging as if someone is constantly playing with the accelerator. Anybody have ideas on what is causing this?

Try lubricating the throttle linkage first, but it is very likely the cruise control amp. Some people have successfully resoldered bad connections on the circuit board. Also, there are reputable companies that rebuild them. Removing the old one and installing the new one is a simple DIY project--search the archives for instructions on your model year. Cheers, Andrew Seidel.

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86 560SEC
85 500SEC Lorinser
83 300D Turbo
75 240D

have you recently replaced any tail light bulbs. Have read that this is a common problem as the cruise control uses that circuit and copper based light bulbs cause this . Read the thread located 4 or 5 posts above yours about the same problem.

Thanks to everyone who had a suggestion to my problem. I replaced the back tail light bulb with genuine mercedes and it didn't fix the cruise problem. I will now try to locate the throttle linkage and lube that. If that doesn't work then I guess it is the CC amp that is the culprit.