Originally Posted by BAVBMW

Thirdly, most cruise systems do not detect an overrev state. In fact, they will cause one. Especially older, 80's vehicles. What happens, basically is if the cruise system detects that the vehicle speed is dropping (let's say you put it in neutral) and applies more throttle to correct (it doesn't know you're in neutral, manuals have clutch switchs in most cases, but automatics have no similar system), there's no load on the engine so it picks up speed at an alarming rate, meanwhile the vehicle is still slowing, so the cruise adds more throttle... You get the picture.

In the case of a slippery road, it's often more the opposite. Once the drive wheels begin slipping, the cruise sees the vehicle speeding up (removing load from the wheels, ie; slip, will cause them to gain speed) so it begins to let off the throttle, this will slow the wheels, but if the vehicle is hydroplaning, it won't neccessarily slow the vehicle. Now when the vehicle reaches an area where traction is availible, the slow moving wheels grab and start to slow whichever end of the vehicle they're on at a faster rate than the vehicle as a whole. See where we have a problem?