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 !!

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