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The IAC on my 2001 F-150 4.6 hums at idle. So far no differences in how it runs that I detect. Just annoying and sometimes loud humming.
Local autoparts store has 3 different manufacturers of new IAC to choose from. 1st is Ford Motorcraft. Which costs over twice as much as the other two (Masterpro and BWD).
I get it that NOS Ford parts are probably best. But times are hard. My question is: Are they really TWICE as good? And of the other two choices, which one of them is best? Or should I just bite the bullet and buy the Ford part?
Check closely, there's a good chance the humming is not the IAC but a hose.
The IAC is a spring loaded dashpot operated by a voltage from the computer applied to it's solenoid to control the opening on a continuous basis to maintain idle within +/-50 RPM.
Also humming noise can come from the EVR if it's filter is dirty and the internal valve is sticking when the EGR is taking in air after being operated by vacuum..
Good luck.
You could try taking it off and cleaning it with carburetor cleaner. Just don't use anything stiffer than a paint brush. IAC was $143, gasket was $1.93, from dealer. At 145K miles I thought it was a bargain.