It depends on where the IAC gets stuck at, if it's stuck in it will actually restrict the air flow, making the idle rich and probably giving your symptom of a low idle RPM and it's fine when the TB is open and letting air in.

Did you run tests on your fuel injector circuit because that could be a possible problem. Check them with a volt meter and they should run somewhere in the close range of 12.6 volts. Also, I'm sure you already did this but I recommend visually inspecting the wiring leading to the fuel injector because this could be causing a short and causing it to misfire. Typically the spot on the rail the injectors are on does not matter, they are pretty universal.

Also, could be your PCM going out and causing it to misfire. I've seen this before and especially when your engine is running lean. I would give the IAC slot a good cleaning out because after time it can get all gunked up and cause it to stick a bit. This happened to me a little while back. I would start with this because it is the cheapest and doesn't take too much time to achieve.

Instructions for cleaning the IAC:
https://dodgeforum.com/forum/1st-gen...ttle-body.html

 

Clean the Throttle Body and IAC really good first off.

Also, I have seen that people have had this issue and taken of the fuel rails to find rust in them. The rust foats back and forth and throws these misc codes.

Did your replace the plugs with Champion Copper gapped at .040?


Next, I would move to the Cam sensor under the distributor cap or Crank Sensor (doubt is a crank sensor tho).


Make sure you reset the PCM after each step! https://dodgeforum.com/forum/1st-gen...ine-light.html