My car has this hesitation stutter while in first gear between 1k and 2.5k rpm. The acceleration sucks as well. My CEL came on and I hook a diagnostic machine up to my ECM and the code read bank 1 sensor 1 too lean. So I changed my a/f upstream o2 sensor, and then got my ECM reset and my CEL went off for a little, after three days it came back on so I disconnected my negative battery wire and reconnected it to turn the light off then with a few hours it was back on. I hooked the machine up again and the same read out came up I know the o2 sensor is installed correctly so I don't know what the hell it could be. There is an abundant sense of gas odor coming from my engine as well as a lag between me pressing the throttle and engine response. I just want suggestions on what is causing this **** because I can't figure out nothing.