Clunky engine, stalling, no acceleration, p2103

Hi folks! Thanks for your help in advance. I've found lots of answers to past problems on this forum already, but nothing on the internet matches the symptoms I'm seeing currently. Here are the facts:

• 2005 Prius, ~313k miles
• Parked for a week with no MIL at the beginning.
• When I tried to drive after that week, it wasn't accelerating correctly. In retrospect, I think I just drained all the charge in the HV battery. I drove a half-mile on a slight downhill, pedal floored, while it slowly accelerated to 28. I heard the gas engine running, but it didn't seem to be doing anything. Then it started decelerating, then I couldn't get it to move at all. Towed back home with the truck.
• Scanned codes and got only one: P2103. I'm no expert on this area, but the throttle body looked fine with the air filter off, throttle moved when pushed open, no obviously damaged wires, etc.
• At this point, I realized the 12v battery was drained and not charging. After charging, I took voltage readings. ~11.7v when fully charged, ~13v shortly after turning car on, THEN the engine started making that awful clunking/shaking noise (possibly a really bad low idle random misfire) and I checked the voltage again; it was down to ~11.4v with the engine still running.
• At that point I quickly scanned the new codes before the 12v died and the car stalled. Two more codes: P0102 and P0113, in addition to P2103.
• The car did indeed stall shortly after that and wouldn't restart without recharging the battery.
• I hoped this would all be solved by replacing the 12v battery. I did that—no improvement. With the new battery in (the codes had been cleared when I switched them) the only code was again P2103, but the engine was still clunky, the engine would not rev, and the car would not accelerate.
• At some point in here I started seeing the "Main Battery" light come on in the nav display. I'm hoping that's simply an effect of the main cause, and that because of whatever electrical/gas engine issue is going on, the HV battery is not charging.

Please advise! Theories, relevant service bulletins/repair manual excerpts, things to test...thanks! I would just replace the throttle body, but I'm skeptical that's the real issue. ECM is another possibility with all these weird electrical symptoms, but replacing that would be a major hassle without more confidence it would help.

 

1. Throttle motor resistance net is normal at 4.1 ohms.
   
2. Wiring harness to ground resistance is within spec (reading "1" on my multimeter at every ohm setting) for both terminals.
3. Wiring harness side to ECM side is within spec for both wires. 0.0 ohms on one side and 0.2 ohms on the other.

Since the throttle plate moves correctly when pushed and all electrical readings are normal, this seems to call for an ECM replacement. I feel like I should take the throttle body motor off and try cleaning/lubing it first though.

I also pulled an old mouse nest off the top of the cabin air filter when I removed the glove compartment to access the ECM...I bought this car 6 months ago ($900 with body in great shape; still think it was a good deal). It had been sitting for a while before former owner sold it and I've already had some unrelated mouse-chewed wires soldered.

 

It is a generic scan tool—MaxiScan MS300.

I took the whole throttle body off today. It looked to be in reasonable shape—some corrosion, but not too cruddy and all the moving parts seemed fine. I've ordered a new used one anyway, and a new used ECM, for $60 total (I love Ebay!) and will see if either of those fixes it.

I had another theory—total exhaust blockage, like from a wasp nest—but no, it's not that either.

 

I agree on testing the old one with voltage. I cut off the plug at the end of the wires so I could separate the wires, stripped them, and tested with an AA battery first. There was a click and it tried to move, but the throttle plate did not move. I wanted to test a 9V but couldn't find one. Then I tested directly to car battery terminals. There were some sparks at the end of the wires, and the throttle plate opened fully.

I wish it hadn't—that would prove it was locked up and I'd be confident the replacement would fix the issue. As it is, probably not. I'll try it anyway and see what happens. It won't arrive til Monday or so. I'll update afterwards.

 

Well, it works with the new throttle body! I think in all my years of increasingly complex DIY mechanic work on old cars, this is the first time I've ever gotten significant help solving a noticeable performance issue from the OBD codes.

The new throttle body has 1.5 ohms of resistance compared to the 4.1 from the old one. Given that spec is anywhere from 0.3 to 100 ohms, that's probably not relevant to the failure of the old one. It must have been mechanical resistance plus electrical resistance. I could push it open, but not easily.

A note for posterity: if you're going to replace the throttle body, make sure you have coolant on hand. There are two coolant lines (one in, one out) that connect to the throttle body, and I lost at least a pint of coolant when I detached them.