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look at the intake manifold you will notice the badge TVIS = Toyota varible intake system. now look below the plenium (top of intake manifold that throttle body is one) and try and look realy good at the intake runners you will notice there are 8 even though it is a 4 cyl, here is TVIS at the end of there runners between the intake and the block is a plate and eery other runner have somthing similar to a throttle butterfly valve in front of it, these 4 runners are shut off during low rpms for more torque, (less are needs smaller area to travel with more velocity) at 4k - 4.5k a small selonoid lets vacume open a small actuator on the TVIS shaft and more air for higher RPM's thats what you are hearing. now take your air box off of your vien air meter and put a cone filter on it, then you will realy like the way it sounds
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