Hi i have a 2000 pport, same as rodeo. I keep getting a p0171. already replace IMG, o2 sensor b1s1.?

At times the LTFT will drop to 0v. on that 1 side bank. People told me a possibility of a fuel filter. I also checked the m airflow. which was very clean. But again i dont see why any of this would contribute to only leaning on one bank. please help.