2003 Prius with P3191

Hello!

I just bought a Gen 1 Prius because it had a battery that was less than 2 years old for basically nothing, drove it home 140 miles just fine, besides partway home the display started flashing white when I took a break, but that went away after a bit of driving. It needed some stuff done, nothing outside the realm of what I was capable of, (tires, a new hood and bumper, probably a bearing, its got some rust, including a small exhaust leak).

Unfortunately, I am an idiot and left a cheap handheld code reader plugged into the OBD2 port for 2 days or so, and when I got back to the car the 12v battery was pretty flat. Turning the key did nothing. I went and jumped it, car started up but with the triangle of death and the display. I had lost my nicer prius aware OBD2 reader, so I ordered a new one and unplugged the 12v battery and left it on a trickle charger overnight. The issue came back when I tried again, I did the same thing until I got the code reader, then drove the car around my neighborhood until I got the triangle again, watching the DR Prius app on my phone, the battery was looking healthy, charging and discharging as expected. engine was running great. It didn't show up until I stopped for coffee, then when I got back to the car and started it, the engine started (I am almost positive it actually did because of the exhaust leak), then the engine just shut off, way more rough than usual, and the P3191 code came up. The display is now really dim and still flashing.

Being a code for the engine not starting, this feels really odd. It was running fine, it started up when the code showed up. The 12v battery sits at ~12.6v when the cars not running. I'd love some help trouble shooting it, I do have access to a nearly complete junkyard 2002, that as far as I can tell was just put there because its battery went bad and the owner couldn't afford to replace it, so if it needs parts thats not a huge worry.