2003 Jeep Liberty Engine stalling at idle and not shifting

I took my car to a transmission place to have it looked at. It seems that my car would stall at idle or if I made a sharp turn. Also, when driving, the car acts like it doesn't want to switch gears. It's almost like it gets stucks in a gear. If I slow down a bit it may allow me to keep driving or it will stall. The rpm's run high at idle when this happens, also. My service engine light has been on. They said that there wasn't anything wrong with my transmission but that they tested the 9 codes in my computer and there was an error read on one of them. What does this mean? Do I simply need them to use a code reader to fix one of the codes. Is this something that I can do myself? Or is it major? Thanks