Im trying to fix my cruise. When I set the cruise control it engages and then drops 5km/h, then speed to the set speed then slows down again. It keeps doing this over and over. You guys got any ideas on how to fix this. This is the old mechanical type in an 82 T/A.

 

Vacuum leaks often cause surging of the cruise control. Not just at the cannister and control itself, engine vacuum leaks can cause it too.