I'm having a problems with my cruise control. It will engage, I can see that the light comes on the steering wheel, then it tries to keep the speed but slowly and slowly loses speed until eventually it's going so slow it stops trying ( while leaving the light on steering wheel.) For example after engaging it will rev the engine up, go from 60 to 55 then slower and slower then 40 then 35ish and it will stop and the engine will return to idle speed. On a side note I've been having problems with whacky vents, changed check valve so that isn't the issue. Any suggestions greatly appreciated thank you!

 

You have a vacuum leak. Could be near the check valve, the plenum gasket, PCV valve, or the cruise control servo itself.

 

Check and repair the vacuum leaks you are experiencing. Check around the intake to see if you have cracked vacuum hoses, especially the ones controlling the cruise control mechanism.