engine light on, code 0340

I put a new engine in my chevy prizm, and now the car dies after you start it, when its between cold and warm, so basically if the car isnt just turned on, accelerating or warmed up. Also the break doesn't work that well if it isn't warmed up. We put new spark plugs in, changed the cam shaft sensor, checked the vacuum lines, and checked the cam shaft sensor circuit. Please let me know if you have any idea.