Engine Hesitation

I have been having some issues with my 2000 Tacoma SR5 3.4L V6 and I'm hoping you all can help me figure this out. Backstory: I have been trying to figure out my error code: "P0171 System Too Lean Bank 1"

I started with cleaning the MAF sensor, cleared the error and it came back a day or two later. One day I decided to put in a fuel additive- probably Chevron brand fuel system cleaner although I'm not sure. One my tank was empty the engine started getting major hesitation when pushing the throttle, sometimes backfires. I tried changing out my fuel filter which didn't fix the error or the problems with hesitation. Once I filled up my tank it seemed to run better- no clue why this made a difference. I'm still working on the error code checklist I'm going through.

I've been seeing a loss of power when I'm driving mostly in 2-5 gears at certain RPM's. I read online the suggestion of changing spark plugs. After changing the spark plugs I now have another hesitation when I press the throttle and hear a noise- it's like a whiff of air at the top of the engine. Video link to YouTube below. Any help is appreciated. Thanks.

https://youtu.be/avQNM9tNslM

 

maybe it's me but I can't hear anything

 

when you first crack throttle your relieving all the vacuum. thats the "whiff" noise.

 

check the vacuum hose coming from the rear driver side valve cover going into the intake tube by the throttle body.

A buddy had a large crack on the ~1/2 inch hose facing the fire wall, threw a P0171 lean code. it sounds like when he let off the gas, the engine was still taking in air for a second or two before returning to normal. It was loud enough that you can hear it, similar to yours.