Engine rpms stay high after pedal release, mpg way down.

welcome!
very unusual behavior. anything we should know about the car? how many miles on her?

first rule of thumb here is to check the 12v.

 

Just a guess and hopefully the experts will chime in soon but maybe a dirty throttle body? Seems like maybe the throttle is sometimes getting stuck or lagging.

 

What is the state of charge (SOC) of your traction battery during these incidents? The ICE will be more involved when the SOC is 3 or less bars.

 

I would try to clean the throttle body first, also check engine air filter as well. If there's no check engine light, its mostly mechanical issues. If there's any sensor issues or ecu issues, it will pop up a CEL sooner or later.

 

I'd second checking the 12 volt battery's condition. I always disconnect the 12 volt when doing brake work, and I notice subsequently, just for the first one or two drives, it'll do odd rev-up, like it's recalibrating something. Might be a failing 12 volt is making this a chronic condition in your car?

Start with just checking voltage with a multimeter, and then if you want to get more DIY in-depth, something like the Solar BA5 can check it's health. Most battery retailers will have something similar but pro-level, and will do a check for free. Or the dealership, for a "modest" charge.

 

you can clean the throttle body yourself, it takes less than 15 mins. We also have a video on our YouTube channel so you don't have to pay the dealership to do this for you. Save yourself some money

 

I have exactly the same behaviour when the battery was too hot or too cold to cooperate, when lift of the throthle the engine slowly goes down with rpm.

 

The only way it might is if either the car or you are subconsciously compensating for the reduced power with more throttle. But the car running the engine more to charge one of the batteries is a good possibility too. If the battery was hot it could have been a protect mode thing. Not sure.

 

weather has been pretty mild up here lately.

 

Hi there,
I have a 2010 Prius with 117,000 miles and for a couple months now I’m having the same weird issue. I was wondering if you figured out why your Prius was behaving like it did?
Thank you!!
Adrien

 

I am having the same issue on my 2011 Prius. Any updates on what the issue is caused by?

 

Seeing similar behavior on our 2010 Prius with 97k miles. Engine RPMs sometimes stay high after releasing pedal. Gas mileage is lower over last couple of months. Engine is also using oil, but that apparently is normal for Prius models of this age.

 

My sister just called me saying her 2010 is doing this. On my way to check it out. We already replaced the engine. the engine doesn't have many miles. I think it might be overheated battery

 

If she's blasting the ac and the soc is low, you may experience this problem

 

Yeah she had the ac blasting, but she said the battery was at 4 bars. She also said the engine is ideling in park, but not even charging the battery because its not low. Odd! Maybe drying 12v? The 12v could possibly be 9 years old...

 

It could definitely be the 12V but if the battery temp is high enough (I think it’s around 116 F) the engine won’t shut off to protect it.