what i can see is that you say the car runs good which means the air/fuel mixture is good. but maybe burning a little too much fuel whch at the same time taking in more air. any scanner that shows datastream will show you almost every important sensor input on your engine that even includes wether its closed or open loop. i have an actron scanner that shows all this stuff. has helped me out a lot in a lot of troubleshooting that cant be fixed with just going by basic stuff.