Now, this is in conjunction with my other post in this forum about my enigne not behaving correctly. Now, i finally got a check engine light and did a code scan and it kicked back the "O2 Sensor, System Lean". Now, I understand that the system running lean would explain the lack of power on take off, or on climbing large hills, or mountain passes. But my question is how can the O2 sensor affect it this bad. Also, i am getting right at 20.5 mpg both in city and on highway. She is a 2.3 with the A4LD auto tranny. How much will this improve my gas mileage and is it really going to affect my take off and hill climbing power. I am so confused by this one sensor. I would much rather everything be as easy as the classic carbed v-8's!