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Why am I getting a loud humming noise (like a horn) at lower rmps from my air intake on a 97 Ford F150 4.6L?

Hello, I bought and installed the K&N Fuel Injection Performance Kit (FIPK) for a 97 4.6L Ford F-150. I installed the kit solely on the directions provided. At times, there is a noise that sounds a lot like a horn on a ship or large boat pulling into a harbor somewhere (as cheesy as that my sound). Anyway, I notice it mainly when there are lower rmps. Also when I start the truck, let it run for a couple minutes, then shift into drive, right after that the noise starts. Also when the noise is goin on, the rpms are raised, almost like the air is gettin cut off and when the sound stops, the rpms drop and nearly kills the engine but it goes to normal. The noise is rather loud too, can be heard over the stereo. And the noise seems to be coming from the filter area, or it maybe could be directed out that way. Any feedback for this matter would be greatly appreciated.

Public Comments

1. This is your Idle Air Controller (IAC). Simple to replace for around $50. It is a small solenoid on the back side of the manifold usually.
2. Yep, that is a moan. It's a resonance being set off in the air induction system. IAC's solonoids have been known to do this. An IAC is idle air control. It provides a bypass of air around the throttle so engine can idle.
3. all KN air filter will make a loud noise due to missing air filter housing. this is one main drawback that KN don"t want to tell you.when you expose an air filter without any insulation,it will increase noise.that is why all car manufactures install air filter case or housing.