I'm having problems with the collision for objects and terrain in maps that I made. Please help if can.
What program did you use to model your stuff? Does using "visual collision" on your object result in any difference? For the terrain - do you mean you fall through it, float over it, or something else?
Are you still in the editor? If you are, close out of it and try again. Also, you didn't answer any of @DuneWulff questions.
A terrain can become intangible if another terrain is added afterwards; BeamNG currently only supports one terrain object at a time. Alternately, terrains can't be rotated and retain their proper collision. If you rotate a terrain, the collision will remain oriented the same way as how it spawned (last I checked). That's all I've got.
the collision messes up when you edit terrain until you exit the editor as for the objects, if you see options set to "collision mesh" try changing them to "visible mesh"