Hey I've got a 99 Ram with a 5.9 Gas motor. I have a P0505 code with a CEL on and for some reason the gas gauge doesn't work when the light is on. My Idle is fine even with the AC on or in gear. I checked the IAC plug with a test light and the key on. Nothing from Ground to the plug on all four wires. From Power to the plug the light is on at all times on all four wires. Seems like the computer is grounding inside?? any ideas?

 

I'd take the gamble and replace the IAC(before dealing with the pcm). Did you check the plug by back probing or removing the plug from the IAC?

 

I unplugged it. The Guy I bought the truck from told me about having to clean the IAC becasue of idle problems but my idle is fine.

 

Replace the IAC, . If that doesn't work sorry for wasting your money. Remove the negative battery cable before replacing or cleaning it if you decide to do so.