I just ran the Motorcraft numbers vs the Borg Warner numbers. Motorcraft shows one for 97-98 (CX1857)and another for 99-2003 (CX1867). Borg Warner shows a 31019 fitting all the years, 97-03.

This is probably your problem. The computer is set to the one you have, and the new one is searching for a sweet spot. I think I would order the CX1867 Motorcraft and stay away from generic aftermarket brands.

Borg Warner (Neihoff/NAPA, all the same) makes good ignition and other parts, but I am not fond of their emission replacement items. Standard, is fairly decent, and Wells, not so much.

 

Well, I just ordered Hitachi from Rock Auto. Let's see how they are and I will report back on the install.

 

Did you try to clean yours first?

Motorcraft Part at Amazon...
https://www.amazon.com/Motorcraft-CX...3Aford%3Af-150

 

Sorry Bink, but that is the wrong number. The OP needs CX1867 for 02.

https://www.amazon.com/Motorcraft-CX...eywords=cx1867

 

Got my Hitachi IAC and replaced. Stable idle and quite down a bit, but there still is a mild humming noise from the engine bay that I cannot pin point.

Regardless, Hitachi IAC worked and it did improve the idle.

 

You never commented on my comment about the IAC horn, Is yours still in place? On 5fours it's about 6" away from the IAC. It's in line with IAC intake tube. It's a silencer of sorts. Without it , it can get loud.

 

Sorry, I missed your quote. I will double check. As far as I know, it wasn't humming before, but started few weeks ago...

 

Thanks for the feedback. Did it appear to be the same as your OE IAC?

 

Yes. When I had the BWD brand, it was not compatible and made the idle fluctuate and worsen the condition.

This one is a direct replacement.