Acceleration Issues - HELP!

Starting in the last 3 days I've had some strange issues with my 2007 Base model Prius (195,000 MILES) and hoping someone can shed some light on it.

Three mornings ago while driving to work (about a 45 minute drive) The red triangle warning light came on, along with the little car with exclamation mark light on the center display screen. Nothing about the way the car was driving changed and I made it the rest of the way to work without concern. On the way home the light was still on, but the car still appeared to be handling fine. I decided to stop at a parts store on the way home to have them check for codes anyway. As the guy came out with the code reader he asked me to crank the car back up, which I did and whaddya know... no light. He tried to read the codes anyway and the only thing he found was P1121: Coolant Flow Control Valve Position Sensor Stuck. When I got home I looked up some information on that code and figured I'd fix it myself.

Next day (yesterday) I go to drive to work again and notice the car isn't pulling away normally, but no warning light came on. It would go, but felt sluggish. It did it pretty much all the way to work at ever red light, but it was fairly subtle. Coming home everything seemed normal for the first half of the journey, then while doing 50mph on the freeway the same two lights (red triangle and car with !) come on and the engine starts revving hard, but the car doesn't pick up speed. I literally took my foot all the way off the peddle and it kept revving while not losing speed, like it was stuck at around 50ish mph. If I put my foot on the peddle it would pick up speed but VERY slowly - like, foot to the floor would make it pick up 1 MPH for every 20 yards maybe. I was doing my best to get to the shoulder and all of a sudden I realize that the car is slowing, despite my foot being all the way down on the peddle. I manage to get to the shoulder and come to a stop. Not sure why, but I decided to turn it off and back on... and boom, everything is fine, except for the lights still being on. I drive another few miles with no issue and get off at the next exit to take it back to somewhere with a scan tool. As soon as I get off the interstate it starts again. Not responding to my foot pressing the gas peddle, revving hard etc. Every single red light I get to I turn the car off and back on again and it works fine for a few minutes, like turning it off reset the problem. Finally get to the parts store and the guy tries to scan for codes - this time with both lights still on - and nothing. Still just the P1121 code about the coolant valve. Was able to drive home without any issues what so ever.

Took it out again last night with a mechanic friend (doesn't work on Toyota's and knowledge of Hybrids is limited just to see if he could figure it out). Everything was fine for about half an hour but just before we got home we lost it again. Around 35ish mph the car just stopped responding to anything I was doing with the accelerator pedal and began losing speed. Pulled over to the side of the road, cut it off and back on, and drove fine back to the house.

Mechanics friend's best guess is maybe the Throttle Position Sensor is going out. Was hoping someone on here could let me know if that sounds right or if it might be something else.

(I should say the hybrid battery was replaced about 5 months ago and I haven't had any other issues until now)

 

The battery I got was a reman 2nd Gen, 6.5 Ah 7.2 Volts from greentecauto. It has an 18 month warranty.

(I tried to post a link to the website so you could see for yourself but it wont let me)

 

I did notice that whenever the warning lights come on the little air vent in the passenger side back seat starts blowing (or sucking?) air. Is this a normal response to the warning lights or could it be a symptom of overheating?

 

My only hesitation in putting it all down to the control valve and an overheating issue is the sluggish acceleration after the car has been sitting, even overnight. I can only assume it’s all related as it all started happening around the same time, but I wouldn’t have thought an overheating issue would have presented itself so immediately in a vehicle that’s been sitting idle for hours. Either way, I’m taking it to a local Toyota specialist on Friday morning (won’t drive it until then) to have him check for any other codes and we’ll take it from there. Fingers crossed for a simple fix!