I have the 171 and 174 codes and also the knock sensor codes as a result or the air/fuel mixture being off. I cleaned the Trottle Body and also the MAF with the appropriate sprays. Ive looked for a Vacuum leak by spraying the flammable TB cleaner on the intake and vacc lines (thinking it should rev up if there is a leak) No results. I can hear a slight hissing noise near the left side of the engine where the Flat plastic Disc is, but have read that it is normal for that noise to be heard in that location. I took the flexable intake hose and plastic Intake tube off and inspected it, No leaks there. Filter is new and clean However, I noticed this Trap Door apparatus on the Air filter Box. I dont know what it is or what function it serves. It is spring loaded and appears to rest on a button or sensor when the door is closed. That button/sensor is attached to some wires that come out of the front side of the Box. Anyone know about this contraption and what is does or what problems could arise if it doesnt function properly? The Car seems to Run smooth enough untill under hard acceleration, when it revs high it stumbles and hesitates. I am thinking maybe that door is for extra Air at wide open throttle and perhaps it isnt openening. The door as a little hook where it looks like the spring should go but it is not in place. Maybe it slipped out of position?









This is the hook (top right of the Spring)-above- looks like something should attach there. Maybe not?



another pic showing the hook on the door

 

It's for extra air flow. I removed mine completely....LOL

 

It's for WOT. Ignore it.

Watch fuel trims to see if you have an air leak.