77 Town Coupe Speed Control Issues

Hi Bill!
I`m from Norway and have purchased a beautiful 77 Lincoln Town Coupe. I have a little problem with the speed control. When I reach a speed of – lets say 50 miles and set the automatic speed control, the speed slowly increases. I was wondering if you could give me some advice for troubleshooting the issue.
I have been told its an issue due to the vacuum system – causes some tubes or leakages somewhere – or is it something else I should been looking into?
Looking forward to your response!
Thanks!
Med hilsen,
Per Rogstad
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Per –
Congratulations an your recent Town Coupe purchase. The speed control does use vacuum but it does consist also of an amplifier, a servo unit and switches which are all electronic. The vacuum system for the speed control can easily be examined under the hood for leaks and cracks etc. but the problem that you are describing is usually caused by a faulty amplifier or the servo in our experience. The shop manual contains a section on the speed control that includes trouble shooting but may not show your exact symptom of slowly creeping to a higher speed in the “set” position. Here at Lincoln Land we sometimes substitute “good known” modules as part of the diagnosis in order to be accurate. Your vacuum circuit for the speed control should therefore be inspected first in all respects. As a courtesy we will include in our advice for you today a copy of the section of the manual that pertains to speed control. We will of course be available to you for further advice or parts etc. at any time.
Sincerely,
Bill