Engine Humming

I have had a reoccurring noise that only seems to happen once it gets Hot outside, sometimes it happens after I turn on my A/C and other times I may not have run it for a few days while driving and it still happens. I will be sitting at a stoplight and my car starts making a loud humming sound, as long as I am depressing the gas pedal it goes away but as soon as I take my foot off the gas it starts humming again. I took it in twice and the dealer drove it for a day and it never occurred while they drove it (of course), but it very annoying and quite load. Any ideas what may be causing it?
99 Ford Explorer Sport (2 Door) V6

Look closely at the Idle Speed Control motor. These will start a harmonic resonance occasionally. Also the hose that goes to the ISC can cause this. Ford has an updated one that has a "muffler" in it to reduce this possibility. The ISC is around 40$ = or -, and the hose is less than 20$

idel air control valve is bad.cost about $50.00 at auto zone.takes less then 10 minutes to replace.i replaced mine a couple of months ago in my 97 sohc explorer.

Would you please let me know if you replaced the idle air control valve or the internal speed control motor and what took care of the humming since my 1999 Ford Explorer SOHC is doing the same thing?

Thanks
Toni



I have had a reoccurring noise that only seems to happen once it gets Hot outside, sometimes it happens after I turn on my A/C and other times I may not have run it for a few days while driving and it still happens. I will be sitting at a stoplight and my car starts making a loud humming sound, as long as I am depressing the gas pedal it goes away but as soon as I take my foot off the gas it starts humming again. I took it in twice and the dealer drove it for a day and it never occurred while they drove it (of course), but it very annoying and quite load. Any ideas what may be causing it?
99 Ford Explorer Sport (2 Door) V6

Love it when they never reply. :banghead:

Could be the transfer case, My truck would do the same thing until i rebuilt the tranfer case and if thats it you'll want to rebuild it too.

Cost of a brand new one from ford= $4600.00 (cdn)
from the wreckers= $850-$1250 pending on the tag #
these prices do not include the $100p/h mechanic

It was actually the sprocket for 2-3 gears (i think) that was damaged as well as a plastic piece on the fork, anyway they cost about $300.00 and I did the labour myself. It was quite a choir but i saved hundreds.

good luck.

As a old Ford tech I've heard the mateing call of a ISC mtr many times! In some vehicles design mods were required to shut them up, but alot of seemingly docile models will let out a bellow when ISC mtr failure is immenent! Also just a heads up! CMP syncro bushings in 4.0 OHVs have a tendency to screech also!

The loud humming noise that occurs when it is hot outside was due to the idle air control valve. I had it replaced and the noise went away instantly. When you replace it make sure to use a gasket sealant and the gasket that comes along with the idle air control valve. I now will have to have an engine tune up performed because the car is idling stronger than normal.