After doing a seal-n-shine on my 3.9 my idle is real low. Here's the seal-n-shine thread....................
https://dodgeforum.com/forum/1st-gen...-the-road.html

I think the factory calls for 500-900 but this thing idles at 400 and 450. Occasionally it'll die when coming to a stop and pushing in the clutch. In addition, it's gutless! Maybe I'm just used to my other cars which are all turbocharged. I don't think there is an idle adjustment on these throttlebodies, is there? Any help is greatly appreciated!

 

Coincidentaly there is, but the screw is covered with a plug. I would recommend checking for a vacuum leak first.

 

The screw that is covered with a plug is not for idle speed adjustment, the PCM is supposed to take care of that in conjunction with the idle air contorl valve.

 

Strange mine idles really high, though by adding different pcm's I got different idle pionts. Mine typically does low low end 900 and up to 1200, and mine is a little scrapper when it comes with power, quite proud for being a v6.

 

Probably like said above your IAC is dead. It is common problem.

 

When I did the seal-n-shine, I think I cleaned the IAC solenoid with brake cleaner. I guess if I unplug the IAC while the motor is running and there's no change in idle, that would confirm it's bad.

 

Unplug it and drive around let it get warm ect, get it to where it normally dies. Then if it is the same then that is your problem. But it may be hard to tell, the engine can idle just fine with it stuck in one position.