Apparently if the TPS needs adjustment and isn't going to the off/idle position, it will set this code. I don't know how smart this pre-obd system is and how to turn that code off or clear it. Or what conditions it clears itself under. But it was defiantly out of adjustment. AC compressor is removed. So depending on what the AC switch is, this could also be the cause. If it is a low pressure switch, removing the AC compressor would obviously activate this. It could be amusing to pursue a little bit more to sort out, but I have other more entertaining jobs to tackle.
With the TPS correctly adjusted I was able to lock the timing. There is a much simpler procedure I was taught on the Yotatech Forum by Jimkola than using a multimeter.
You remove the throttle body and loosen both TPS screws. Put it back on, loosely tighten the top screw. (You can't get to the bottom screw safetly with the throttle body on. And use QUALITY screwdrivers to break them free, they are usually stuck good.)
Start the truck/car up get to operating temp. Insert jumper. Rotate the TPS and watch timing. You will see it stabilize, rotate until it jumps, then turn it back ever so slightly until it stabilizes again. It is a noticeable difference. Lock the top screw down snuggly. Shut down, pull the throttle body back off and tighten the bottom screw.
I would add that you probably should replace the throttle body gasket. Mine tore but I left it alone and put the TB back on. No sealing issues. A thin smear of RTV would reseal it well enough too until you could get a new gasket in hand.
So I was able to get my timing locked in and sorted out. It was almost 40 degrees advanced!!!!!!!!!! And the engine still pureed happily like nothing was wrong. Crazy.
I think without the jumper, rest timing was at 15 degrees. With the timing locked it is set per the sticker on the hood. I think mine said 8 but I would have to verify. It was a couple weeks ago now.