Be careful with the K&N and other oil saturated filters. They have been known to cause MAF failures in the past because the sensor gets gunked up. If you go to www.bobistheoilguy.com, there have been independent tests showing that the paper filters do a better job at filtration than the K&N's do.
I agree with Dookie's post. The K&N will flow better, but it does not filter as well. And I have also heard how the oil can gook up the MAF sensor.
I will offer this much though - I've used a JWT Popcharger (i.e. a big K&N cone) in my 97 Maxima for 6 years now and had no problems with it. I say "had no problems" because last month the MAF sensor went south and the car was stranded. I am not sure if this is related to the oiled filter, since my mechanic said the sensor was not contaminated with oil. I suspect the MAF sensor failure was unrelated to the K&N filter in my case, and would not hesitate to use it again in the Murano if there were ever an application for it.
Very few Nissan dealers offer K&N filters, and I am not aware of any official Nissan NA website that offers K&N filters. I believe Courtesy Nissan (a fantastic dealer) offers these parts but thats one of the few dealers that will probably repair an oil fouled MAF sensor. I doubt your local Nissan dealer will do that - its unfortunate not every dealer is as understanding of aftermarket mods as Courtesy is.
I agree and disagree. Ive had K*N filters on my last 7 cars. I put them on after a few thousand miles and Ive run 5 of them past 170,000 miles and never had a problem gunking up the MAF or with filtration. There was never any dirt or dust etc in the intake trac and none of my cars ever used any oil. (if your filter isnt working and your engine is eating dirt your rings will be the first to go). I change my oil every 3-5,000 miles depending on use and use mobil 1 synthetic. IF you over-oil the K*N filter and really soak it, then yes the MAF Can get coverd with oily residue and therefore will become less sensative. If you think its a problem, you can gently clean the MAF sensors inside with a Qtip and some alcohol.
I hade a K & N installed by the dealer in my MO 1000 k ago and have had no problem. I have had one in my last 4 vehicles and find the results minimal but overall cost effective. I did have problems with the cone filter (cold air induction) in my last truck (Durango R/T) when I over cleaned applied new oil...to much. I experienced low RPMs and stalling for the first 200 Km.