Gen 2 2007 revs up on releasing gas pedal

Hi all,

I have an unusual issue with my 2007 Gen 2 Prius, it has been regularly mantained, 150k km (93k miles) and without any issues until recently.

Yesterday I noticed, that when I let go of the gas pedal, I can hear the car engine working more loudly instead of it either working with less intensity or completely turning off. So, lets say I'm driving at 80 km/h (50 mph) and when I let go of the gas pedal, the engine starts to be more loud and it revs up, as if you were driving in 3rd gear downhill on a regular manual transmission car. I tried reproducing this issue multiple times with success. So the car works on higher RPM instead of a lower one. This happened regardless of the speed at which I was driving. Everytime this happened, if I stopped and turned off the car, and then turned it on again, the issue would go away.

Has anyone else experienced a similar issue? Do you know what might be the culprit?

 

The gear selector was in "D", not "B". The engine was running when I let go of the gas pedal but the current fuel consumption reading was 0 liters. Cruise control wasn't turned on. No warning lights were showed on the dash. As for the car battery, this is the first one, it was dissassembled and thoroughly cleaned 2 years ago, and new copper plates were fitted. The battery was in excellent condition (looked like new, and in general the battery health readings were fine). The battery cooling system was also cleaned. I don't think the battery degraded in any significant way, because that would reflect in the fuel consumption - the fuel consumption was normal, as well as the general performance of the car, and the battery was charging just fine. 95% of the time the battery charge is at optimal level (blue bars), very rarely at high levels (when driving downhill), and purple bars almost never. When this issue occured, the car's computer showed green bars (one bar above the blue bars boundary). This did occur when driving downhill (however the incline was not steep). I was driving on much steeper roads where battery charge levels would be well in the green bars range and this wouldnt occur. When I pulled over, turned off the car, turned it on again, the issue disappeared. I have now made 200 km since this issue went away, and it hasn't reappeared since.
I'm not entirely sure as to what might be the culprit here...