New to Forum - had this Gen-3 Prius 4 years

Greetings!
New to the forum, did a 'search' for what's happening with our Gen-3 (2010) Prius to no avail
Yesterday we had the infamous "rough start" only the worst episode ever ... REALLY rough and longer than previous episodes, followed by extremely high idle speed for a moment or two. Afterwards, it seemed 'business as usual' and down the road we went. (Background: I'm NOT a hyper-miler, I am a HIGH-Mileage, self-employed, sub-contractor - gas is my biggest expense, therefore the Prius.)
About an hour (and 20-something miles) into my day I noticed the ICE was running more-or-less constantly. This continued in spite of shutting it down several times. It's 'possible' that the "Power" button had been accidentally activated - didn't notice particularly. Later in the day, it finally occurred to me to press the "ECO" button, which seemed to resolve the issue (the ICE immediately stopped running and went back to 'normal' operations).
Got back on the road again today and an hour into my day the same symptoms (ICE running constantly in spite of battery status, even while sitting at red lights, stop signs, etc.)
Can't seem to find anything on the forum (except the HV battery cooling fan - which appears clean and functioning) to explain this erratic behavior. I 'know' this car, I've put 120,000 miles on it since spring 2014 and it has never performed this erratically and with such poor gas mileage (dropped from low-40's to mid-30's mpg).
Any suggestions would be greatly appreciated!
Peace,
J n Pj

 

Nearly new ... less than 8 months, dealer-installed.

 

Thanks for your interest!

Mileage: 187,700 this fine Florida morning

The fact that I had to Google "egr circuit" makes THAT answer self-evident ... but for those slow on the uptake (see what I did there?), we have done NO maintenance on the EGR Valve or Cooler - didn't know they existed , nor that they could be a cause of our problem

The only 'base line' we have for HV battery cycle is the pre-event performance, which is to say there have been no indicators of HV battery problems. Post-event, the HV battery symbol/icon on dash remains at approximately 3/4 as the ICE continuously runs. When "EV" is engaged (which we had never done pre-event), it seems weakish, e.g. a couple hundred yards of level-ground, snails-pace travel and it 'kicks over' to ECO.

Thanks again for the kind (and prompt!) inquiries. (FWIW, I 'used to be' a shade-tree mechanic, but "Time is Freedom" and we have a trustworthy mechanic that we're taking it to this AM.)

Will keep y'all posted

 

Hey Y'all!

Again, thanks for the prompt and courteous replies!!

Took 'er to the trusted (non-hybrid) mechanic. He referred us to Toyota as he can't get any fault/trouble codes and doesn't want to "throw new parts at it until something sticks!" (THAT'S why we trust him!). I told him what was said about the EGR, he said it tests "no error".

Further discovery: first out of the gate in the AM (before she's warmed up) operates flawlessly as before. After the warm-up, (about 10-11 miles) it starts reverting (ICE running constantly regardless of all other parameters).

I don't have time to monkey with EGR or anything else ... guess I'm stuck with Ployota Unfortunately, we've had less than stellar experience with the two dealers closest to us (outright LYING by one, shady principles by the other ).

Wish my grandson was closer - he's a natural-born wrench-monkey and would be delighted to get to the bottom of this!

Peace, y'all