Jibby,
K&N are oiled filters that kill MAF's.
They may flow good amounts of air (which usually indicates they don't clean it as well) but they will cause grief with you MAF.
I'll second that. I have a K&N on my Holden Commodore - similar MAF setup. It uses a precision restitance to measure air flow.
I used the recommended oil and in the recommended quantities in the K&N. Car went well for a while then started to hesitate on moderate acceleration. After a LOT of time spent investigating, I noticed a fine black oily powder in the air inlet. I used carby clean in the throttle body etc, and it did improve things (I suspect cleaning out a lot of older gunk did that). But still had that hesitation.
I reasoned that the oily power came from the K&N, so i removed the MAF sensor and closely examined it (microscope). I could see the same oily powder in it as well.
I used an electronic cleaner - I could SEE it was cleaner and could now see the actual body of the resistance.
Needless to say, the car ran much better.
I still have the K&N because in my case it did make a significant difference over the standard filter (but it's not a 1UZ)., but I am much more careful of the amoungt of oil, and the cleaning of the filter schedule now includes a MAF sensor examination.