Lately, since it has been cold, I have experienced a loud humming noise eminating from the engine compartment of my 2000 Mercury Marquis LS.
It lasts for less than 5 minutes, and disappears after I start to drive away.

From researching this issue on the internet, it seems that others have experienced the same, and suggested that the cause is the IAC and to clean or replace it as the fix.

Can anyone describe where it is, and provide a link as to how to clean or replace it?

Do most of you clean or replace it?

 

I also talked to the service advisor at my Ford dealer.

He said if the IAC were to fail, the car would appear to want to stall out or idle roughly. My car does not display these symptoms, and runs smoothly.

He suggested that it could be the electric fan kicking in too early, some solenoid or sensor.

Could it be the FAN and not the IAC?

 

This morning when I started my car cold, after it fast idled for a few minutes, I started to hear a fog horn noise eminating from the air filter box.

I decided to replace and install the IAC Valve today myself buying the part from my local AZ based on all the recommendations that I have read about this particular problem on the internet.

It was easy to remove and install except for the lower bolt that fastens the valve to the throttle body. It was a pain to get to with my ratchet and extension because of the way the valve is horizontally positioned at the rear of the engine. With the help of the AZ manager, we finally were able to loosen that bolt on the old valve, and tighten it on the new.

Started the car, and so far no noise.

Hopefully, this works as the solution.

 

Its been 5 days since your last post. Has the noise come back since changing the IAC ? Or did that do the trick ?

 

So far, no noise but I have only used the car two out of those five days.

 

I recently had a similar problem with my 2000 LS. I changed the IAC, with an after market part from Advance Autos. It didnt work. Even more searching I found that the IAC tube was the problem. I replaced it with an older model Cougars IAC tube with a muffler. I used the the soft rubber elbow from the old 1 to stick it on there. Its ugly and not a prefect fit but its been a week and a half, and I havent heard the noise once.

Just incase it turns out to be something else.

Good luck I hope you found the issue already.

 

Thanks Larry for the tip.

Since I installed a new IAC from AutoZone, I have used the car a few times, and so far on cold start, no noise even when the temp was in the 20's. So maybe that was the problem.

As you probably know, that second screw at the bottom of the IAC valve is a pain to get to, otherwise installation is simple.

 

I'm having the same noise in my 99 grand marquis. It's very loud. When the humming begins and I sit idle, the engine will die.

After reading this thread, I'm going to replace my IAC as soon as I have time for it. Will update on my results! Thanks.