Sounds like you got your phone wet. You'd have to ask Tony - one of our Moderators - why this happens, but, some how or another, you've gotten it wet, or at least damp.
Pull the battery out of the phone (while the phone is on), and check the battery. On the bottom there should be a very small round hole. Look inside it and tell us what color dots you see....if any.
While the battery is out, clean it up inside and out real good. Also, of course check to see if there are any sign's of moisture about and clean that up.
The reason for pulling the battery out while the phone is on is making the phone do a hard restart. It's almost does the same thing as if you hit the power button on your computer instead of going through the proper shut down procedures. Makes the phone do a complete recycle of itself. This seems to help clear up a lot of problems.
If nothing seems to help, and the phone keeps going into Car Kit Mode, you may have to replace the phone. If that's the case, I sure hope you have insurance, as the first thing the tech's are going to do is check for water damage.