im installing a K&n cold air kit for my friend right now my car was already modded a little bit whne i got it so i never experienced what to do with the stock air sensor that is attached to the stock intake what do i do with the sensor disconect it or leave it there with the new cold air kit.

 

You mean the sensor (IAT) connected to the intake elbow? The K&N (or any other CAI kits for that matter) doesn't replace that elbow, so leave it where it is.