E350 with a moaning sound

Looking for some thought as to what the issue might be.
I have 94 E360 with a 460 engine (motor home). The RV stars and runs fine. The only thing is when the RV gets warm
(driving for about 20mins). It randomly will make a moaning when idling. If you rev the engine up it will stop most of the time.
I know it's not the fuel pump. It in the back. This sound is coming from the engine.
I was told it might be a IAC vale. But before I go off and buy a $75 part. I wanted to see if any one might have another thoughts or agree that it is a IAC value.
If it is a IAC vale the question I have... Is it used more or less when the engine is warm?
Let me know if you need more info.
Thanks !!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.