'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.....

 

Finally Fixed it!! Not a vacuum problem, but a corrosion problem at both electrical connections to the vacuum solenoid. Cleaned them and put some dielectic grease...voila! Problem all gone. No one had any help for me, but maybe this will help someone else!

 

Thanks for sharing the fix.
We need more of that on this forum.