cruise control issues

[crhenkel]

My crusie control in my 1986 190E 2.3-16v is surging back and forth. When I set it the car will stay at the speed set for maybe 2-5 minutes at best before it starts to surge. It will do small increases in speed, speeding up and slowing down say amybe 1 to 2 miles an hour, back and forth.
I need to know if anyone thinks it could be something other than the crusie brain box, the controller in the passenger floor board? I have done some checking and found that the control box solder connections will deteriorate and need to be resoldered, I have done this once and the car seemed to be better for a while and now it is doing it again. I am considering ordering a rebuilt controller, but I want to be sure it isnt the cruise actuator or something other than the controller first. There isnt much to the crusie system that can go wrong. Any opinions?