P2118 Throtle Actuator Control?

Hi I've been using this site a lot to help in the restoration of a used 07 Gen II, so first I just want to say thank you to the Prius gurus here. However I've finally run into a problem that I couldn't find a specific thread about, so here's the story so far...

Picked up the car for next to nothing from a friend. He parked it one day and it just wouldn't turn on anymore, even with a jump. Thinking it was probably the traction battery and possibly the 12 volt that needed to be replaced. (It has 200K miles on it,) I did some thorough research and tinkering and found that the fuse linkage was blown. I replaced it and jumped the car and I finally got it to turn on but with the big red triangle of death and the engine would make some buzzing but not kick on. I trickle charged the 12v which got the engine to finally kick on, but then die after a few seconds. I hooked up a code machine and got two codes: One for the traction battery and the other was P2188.

I took apart the traction battery and replaced the bad cells, (using many helpful posts here and some videos,) then slapped everything back together. Eureka! The engine finally kicked on and stayed on. No more triangle of death. I proceeded to take it for a test drive but much to my disappointment could not get over 20mph!

I hooked the code machine back up and only P2188 remains. I've seen so many conflicting ideas on what this code could mean. One clue that may help is that the radio periodically changed volume once or twice when I was driving it around the neighborhood. This is a real head scratcher, any help on how I should proceed is greatly appreciated!