ICE revs while coasting and when car is stopped

My 2004 Prius ICE seems to rev a lot compared to my 2006 Prius. It revs while I'm coasting at low car speeds (eg 30 mph), decelerating, and even while the car is stopped (power "on"). What controls the ICE speed? Could somethign be defective (MAF sensor, speed control circuit/ECU, etc)? I repaired the front end after a collision took out the inverter and inverter pump, air inlet box, radiator, fans, air bags & seatbelt retractors, etc. I replaced both aux & HV batteries, mainly due to them dying while the car was parked 4 years.

 

I forgot to mention that while the car is stopped (in gear, I believe) and the ICE is revving, it will slow down to a "normal" speed if I press down the gas pedal slightly and hold it there. When the 2004 Prius ICE revs, it sounds like my other (presumably normal) Prius does only when you're accelerating hard or climbing a steep hill and need the extra power. It is revving pretty fast, probably about 4000-5000 rpms (my guess).

Any suggestions would be greatly appreciated. I don't see any dash/MFD warning lights. Don't know about codes; don't have a scanner to check for codes.

 

Wanted to check some things myself first, before paying for a scan (and possibly a tow). What gets me is why the ICE stops revving as soon as I depress the gas pedal very slightly and hold it there. Whatever circuit sets the ICE speed, am I bypassing/affecting it by holding the gas pedal down a bit? Thanks!