Cruise Control Problem
 

'87 Coupe DeVille. I have a recurring problem with the CC. No codes. The switch-test shows them working properly. The problem occurs when I either turn the engine Off or disconnect with the brake pedal. What happens is that it won't hold a steady throttle afterwards. Upon 'resume' it gets back to speed, then immediately throttles back. This action keeps up until I turn the CC Off. Turning it back On (at the CC switch), only continues the behavior. Prior to that it works perfectly. Could this be an electrical input/output problem with the VSS? What is confusing me is why it works properly when I first turn it on, then it doesn't. Might there be a vacuum problem? Thanks for any info.....