How to set down idle speed on 1996 Ram 3/4 ton 5.9 gasoline engine?

[nothingbutdarts]

My new to me 1996 5.9 when first started idles about 1050 RPM then drops down to about 850 RPM after say 20 seconds, it does this hot or cold, it sure would be nice to have it idle around 650 or 700 RPM, any suggestions would be appreciated, Thanks!

 

[Mop]

Sounds like the Idle Air COntrol sensor is bad. Right behind the throttle body.

 

[65 sporty]

There's a lot going on to control the idle speed. Yes the IAC motor controls it, but the PCM commands it. Check for vaccum leaks first.

 

[nothingbutdarts]

^ ^ ^ ^ ^ ^ So if I check & do not find a vaccum leak, where would a person look next? What is the best way to check for vaccum leaks? I have heard a unlit propane torch/starting fluid/acetylene & so on.
Thanks!

 

[Mop]

^ ^ ^ ^ ^ ^ So if I check & do not find a vaccum leak, where would a person look next? What is the best way to check for vaccum leaks? I have heard a unlit propane torch/starting fluid/acetylene & so on.
Thanks!

Simple brake cleaner will work. We don't want to go flammable
You can also turn the oil cap upside down, see if it sticks to the oil fill opening. Spray around the vacuum lines. Spray at the Plenum intake manifold. Just quick shots, nothing sustained. Listen for changes in the RPM's.

 

[AJ.]

If you do not find any air leaks, and the exhaust smells normal, then some IACs are adjustable as to the minimum opening. The Idle-speed is still programmed to target a certain number, but by closing the IAC, you may get a better result.
But you gotta prove absolutely that all the air entering the intake is going thru that IAC.