Originally Posted by mpich
Could the new K&N have thrown some oil or something on the MAF sensor?
When did you put the filter on in relation to your problem starting?
It could certainly be the trouble but there could be other causes. It'* not uncommon to hear of this after a filter install or clean and oil. Excess oil could be picked up in the air stream and deposited on the MAF sensor. In that case the MAF will not read the incoming air correctly and will report much less air than is actually flowing, in that case you would certainly get a lean condition.
To clean the MAF, once your intake assembly is removed, you will need to remove the MAF screen. You will need to remove the circlip around the perimeter, you can do this gently with a small screw driver to pry towards the center. Remove the MAF screen by very gently prying and edge or two and wigling it out, the screen is somewhat solid but can be easily damaged.
Use a Qtip with Rubbing Alcohol to clean the MAF wire, be extremely gentle because it'* a very small wire. If you need more details on this post back.
Otherwise, you could have melted a wire for your O2 sensor or it chaffed against something. Also, the sensor could be defective. If it does need repalcing, only use an AC Delco unit (AFS 109), other brand are known to be less effective.
Hope this helps!