Cruise control

I'm sorry I can't help with your problem, but I have a similar problem on my 1994 Volvo 850 wagon (5cyclinder automatic, not turbo). In the morining on the way to work the cruise control usually works fine, but in the afternoon on the way home it almost NEVER works! Someone said that it might be a vacuum leak, and that makes some sense, I guess, works when cold but not when hot. I would appreciate any help on this matter.