Cruise control question/problem
 

I have a 79 911 with cruise control. The cruise control works, but it will chase the set speed I.e. If 65 mph is set, the speed will fall about 5 mph (60 mph) then speed up to about 67 mph then slow down again and start the process over. Is this the control module, maybe a vacuum leak or something else? Any help will be appreciated.

I replaced the spped control computer in the trunk of my 85 911 and it now works fine. My car would not hold the set speed. I bought the used unit on ebay for $45.00