Back in the early 2000's it was posted on all the major diesel forums that Ford as canceling warranties if they saw a K&N filter in your truck. My modified 7.3 flows a lot more air than any 4Runner, so in no way am I trying to say that a K&N shouldn't be used in the 4Runners. I also don't believe everything I read on an internet forum. But if use a quality company like Blackstone for UOA's they can tell you how well your air filter is doing or how bad by certain levels in your UOA report. I don't have one of mine in front of me, so I can't say which reading it is. I also remember many of the members of the Diesel Truck Club I was in were running the K&N open element filters and several of the filters had large holes form after a short amount of time. For that reason alone I will never run a K&N in any vehicle of mine. I'm certainly not racing or towing heavy loads with my 4Runner, I have specific vehicles for needs like these. Stock airbox and a quality pleated filter, I prefer WIX, and a complete UOA done every 3rd oil change will help my 4Runner and my other vehicles to out live me. I'm old as dirt, lol!!!!!! YMMV?
NCH