I posted pics mostly of OBD readings and a video of engine attempting to run normally.
Microsoft services
Information:
1. Per the upstream O2 sensor: it wouldn't come out and the wires severed at the tip so I disconnected it. I tried connecting another one and covering it, but it doesn’t change anything. At some point I'll replace the header/sensor but I doubt that's the source of all this erratic behavior. It should be running open loop without the O2 according to my research.
2. Cooling fan errors can be ignored: I jumped the relay to switch them on when I see fit because otherwise they don't come on til 225 or whatever it is which is too hot.
3. Replaced VSS (502 error) with a junkyard part but nothing changed at all.
4. I looked all over the wiring harness for exposed wires and shorts, only place I found that was by the PCM and some of them looked like they had been eaten by a rodent. I repaired and shielded them but the only result was the speedometer came back online.
5. The TAC 2107 and solenoid 1860 errors I thought would resolve by fixing problems with the wiring harness but car still running poorly, as said nothing much changed.
6. Low beam relay was clicking every time battery died, and still did that after I swapped the 8866 relay. Low beam headlights keep going out very quickly. I get them from the junkyard but they burn out about once a month. I don’t see a wiring problem visible there either.
7. Battery normally checks at 12.6 when not dead, and 14.6 while car running. I tried to drain test by bridging connectors with terminal on amp several times and each time there's miraculously 0 load, even when I open a door or turn on the key. I also pinned the meter on both sides of each fuse and none had load with car off. All of which seems impossible, since the battery drains and usually doesn’t start without boost, even minutes after running for a while.
8. It's a 2004 Grand Prix with 195k miles and I'm the only mechanic I can afford. I can’t afford a new car either. This is it.
Problems still existing:
Engine RPM fluctuating drastically, except when idling after a minute of warmup (tac?)
Sputters on acceleration without delivering much power (tac?)
Hard time starting especially when battery mysteriously drains (solenoid?)
Battery keeps getting drained or shorted. (no idea anymore)
.
Anything you know that will help is appreciated.