Cadillac Repair: 1994 cad deville, o2 sensor, gas mileage

Question
car became hard to start and gas mileage decreased. after a few day the engine started surging. computer said bad rear o2 sensor changed it and no improvement. any idea's. thank you. ron

Answer
After you replaced the sensor did you CLEAR (erase the CODE from the computer ?.

Run the diagnostics again and when the ocodes start to appear tell me EXACTLY what displays on the screen EXACTLY as if you were video taping it.

Check your fuel pressure.