Help! New Engine Noise

[1997ThunderbirdLXV6]

In my defense, it was more of a Barbie hammer.

Meanwhile, this is me removing the MAF sensor for cleaning:

 

[XR7-4.6]

Meanwhile, this is me removing the MAF sensor for cleaning:

I always preferred that directors cut


As for MAF cleaning this is more my style

… yes I have a K&N air filter lol

 

[1997ThunderbirdLXV6]

… yes I have a K&N air filter lol

And K&N stickers everywhere?

 

[XR7-4.6]

And K&N stickers everywhere?

They only gave me one so I’m too non-committal to apply it

 

[supergordo]

Here is my 2 cents. If it makes that noise again I'd give the IAC a good smack with the handle of a screwdriver. If that doesn't change things. Unplug the IAC while it is running. See what happens.
And while I just told you to hit the IAC. I don't disagree with Kevin about NOT hitting things with a hammer and listening with a long screwdriver. The listening technique works and does help.
That does not sound like a bearing noise in any case from my point of view.
And someone else suggested the PCV. I have absolutely replaced PCV valves for customers that have made that noise.

 

[1997ThunderbirdLXV6]

. Unplug the IAC while it is running. See what happens.

Did that this morning. Unfortunately I wasn't filming. The engine died within two seconds or so. I think the rattle did  not stop immediately when I unplugged the IAC valve, which I guess would suggest that the IAC isn't the issue.

Nonetheless, I just replaced it with a junkyard unit courtesy of a '99 E-150 4.2; at least that way I can rule it out. Plus my stock IAC has been known to be on its last leg; a year ago, it kept me from starting the engine, but then worked again after a good cleaning.

The E-150 valve has some major corrosion of the housing, but at $12 it's worth a try. At least it's an OEM Ford part.

And someone else suggested the PCV. I have absolutely replaced PCV valves for customers that have made that noise.

That was literally the first thing I replaced after buying the car three years ago. Granted, that was a cheap Autozone unit. And I didn't even know why I was replacing it; I just wanted to do something, and that was easy. I still have the stock PCV valve somewhere.

 

[1997ThunderbirdLXV6]

Three days in a row, I started the car early in the morning, in coldest possible conditions, and no noise was present. One could assume that the swapped IAC solved the issue, but I'm skeptical since unplugging it the last time the noise was present did not stop the noise instantly.

Meanwhile, it's been dry for days. Now it's raining. If it's an electrical arcing issue, humidity may be the deciding factor.

 

[bowez]

Revving up and then going away makes me think IAC.
Might be time for a new one.

 

[White Lincoln]

Meanwhile, this is me removing the MAF sensor for cleaning:

I hate when that happens....

 

[1997ThunderbirdLXV6]

This particular noise hasn't occurred in weeks. It seemed cold/rain related, so I may come back to this thread next winter. For now, knock on wood, all is well.