what is mentioned above is what is generally refered to as MAF turbulence....
the EVO i have been tuning on has had the same issue with the K&N on it, we added a shroud around it, and solved the AF ratio jumping around...
of course, alot of the ebay intakes have different size piping, and since the WRX uses a drop-in MAF, there is more air flowing in the car than it is calibrated for, causing the lean condition.
class dismissed.
