I have a friend that has 454 EFI that the starboard engine won't idle below 1800 rpm's. Changed the Oxygen sensor, no different. When it goes below 1800 RPM' it just dies, other than that it runs just fine. Any suggestions?

Take to Merc dealer that has the elecrtic device to check your
engine saving you a ton of money buying parts without knowing
the cause.

Sounds like the typical symptom of a vacuum leak.

Yup!

Thanks, we'll look for a vacuum leak.

do they have a idle control solinoid like car's?