Hey all New to the forum but not jeeps! I've got an issue and I'm having some trouble attempting to narrow it down. Recently purchased a 98 XJ. 4.0, Auto, 221k on the odometer good price. Bought it with a no start condition, did troubleshooting and found it was a bad CPS. Starts now, runs and drives and have done a few upgrades to it. My issue is there is this persistent P0505 code that I can clear, start it up a few times and then it comes back. Jeep doesn't have a high idle, in fact whether the IAC is plugged in or not it will idle at around 750 on the tach. I've had it running no CEL, UNPLUGGED the IAC and it does nothing. No idle change, doesn't surge, throttle response is the same. No surging and as far as I know when the CEL is showing in the cluster the jeep drives the same? Maybe is me thinking it drives differently because there is a CEL in my face but idk. Throttle response is there, no high idle possibly a slight miss? but the thing rattles already so meh?
Here is a list of what I've done so far to try and find the issue.
-Changed IAC.
-Traced the connector and wires back to the PCM to ensure the insulation on wires isn't cracked or there is a short.
-Ohm checked the Wires to the PCM and to ground to ensure there isn't an open.
-Volt checked the wires to ensure they're receiving the proper 12V with key on.
-Ohm checked across the IAC to ensure nothing was shorted
-Sprayed each vacuum connection I can find with Carb Cleaner but no idle changes.
-Sprayed around the TB and it's connections as well as Intake Manifold to try and find a leak, no issues there either.

I'm at a loss as to where the issue could potentially be. Perhaps it's an intermittent issue that shows itself once the engine has warmed up? I've had an issue with my CJ where the 12V fuel pump power was breaking down when it was warm SOMETIMES and that was an issue to troubleshoot, but this is a strange one. I can start the jeep, have the CEL immediately pop up before engine is turned on, clear it, and it won't pop back up until randomly later. Usually about 5-8 restarts is when it pops up, clear it and it'll be like that till again 5-8 restarts. Super random.
It's the only code that pops up, nothing else and as much as I tell myself eh it drives fine don't worry about it, can't leave well enough alone and having that CEL pop up randomly bothers me.

Below are what I used to check wires for the circuit.

 

So I've now had more time to do some troubleshooting and have ran into some interesting stuff.
checked voltages with Key On Engine Off at the IAC connector.
-Pins 1-4 read 12V and pins 2-3 also read at 12V.
Here's where it gets funny.
-Pins 1-3 reads at 12V and Pins 2-4 read at 12V.
-Pins 1-2 read open and Pins 3-4 read open.

Weird right.
So we go to the PCM, remove C1 and start probing the actual PCM and check the pins from the PCM. Pins 10-11 which is suppose to control one side of the circuit only shows .77V with the Key On Engine Off. Pins 19-20 show 1.21V. I've also checked the pins with each other for OHMS in the 200 range and they read 1 so im seeing that as OPEN which they should be since they're not connected.

I'm now starting to learn towards a bad PCM? Any thoughts? Thanks fellas!