Engine dies when I let off gas

I have an 02 Mercury Mountaineer. It won’t start unless I hold the gas down and as soon as I let off the gas it dies. Any guesses? Thanks.

Well a very good gues would be a sludged up or defective IAC/idle air control valve.

Some folks have good luck with simply cleaning the IAC. Or for about 60 bucks you can buy a new one at Napa or Autozone. Replacing it takes about 5 minutes.

Heres a link with everything you ever wanted to know about the IAC