Review on K&N Engine Air Filter: Premium Performance Replacement (Land Cruiser, Tundra, Sequoia, LX 570) by Kenny Loeslein

This product works like a regular K&N filter - it saves you money on filters in the long run and (in my experience) slightly increases mileage and improves throttle response. However, unlike all the other K&Ns I've used, installing this unit definitely resulted in the whistling noise that others have been talking about at around 2000 rpm. It's not loud enough to drown out the radio or similar, but when the radio is off you're definitely there (especially with the windows open). Fortunately, the reason for this is known and the solution is simple and cheap. A seal with an integrated screen is located behind the throttle valve. Toyota makes the same seal without a strainer (available here on Amazon for about $7). Part number 22271-50050 - took about 5 minutes to install. You simply remove the throttle body (4 x 10mm bolts), remove the shield, put in a new gasket and bolt the throttle body back on.