I have a 1996 Dodge Ram 2500 Diesel. When I set the cruise control it locks as it should. Then it starts to accelerate. I can slow it down by pressing the coast switch. As soon as I release the coast switch it begins to accelerate again.

 

normally it is the srevo, it sits under the driver side battery and over the years, battery asid finds its way inside and raises all kinds of hell with the servo