Cruise Control Problem
 

I have a problem with the cruise control on my 2001 X Type 3.0 auto.
When the cruise control is activated, the car accelerates to 4 or 5 kph about the actived speed then settles back to the set speed. This also happens on "resume".
So I'm just looking for someone who might have a possible solution. I've been told it might be a vaccum issue, but if so, where?