01 5.4l whistle, erratic/high idle
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It's not really the FIPK K&N , but a Throttle Body spacer sometimes and a larger throttle body , I have the high pitched whistle and it is due to my PowerAid spacer and also on the K&N Generation II if you take out the tube like they say to it will also whistle it is optional in the directions, if you put it back in it will help but won't eliminate it, due you have a spacer or larger mass air flow or larger throttle body