A few people on here including myself have had this problem. I had both O2 sensors replaced at the dealership and after about 6 months I started getting a CEL when under load and the car was almost fully warmed up and it would be a code 32 and every once in awhile a 37. I know my cams are in time and so on. I haven't had a CEL in about 3 months now and what seems to have done it was Svxfiles putting up my new exhaust. I only got the CEL once or twice right after he put the exhaust on and haven't had one since. I'm thinking maybe an exhaust leak was causing it, So check your exhaust for leaks before the O2 sensor and right after them at the cat. converter/Y pipe. My Leak was at the third cat.
Good luck. Jason