Hi, first time posting on here. The car is a MY04 GT liberty 5spd. Lately when driving with cruise set the motor is hunting and you can feel the car lurching. It runs fine otherwise, although idle speed hunts occasionally (always has). I've read 02 sensors can be a problem but there is no CEL. Only modifications is cat back exhaust. Can anyone help or is the best option to go to a dealer with diagnostics?