Delayed engine engagement coming off electric

Are you current on all maintenance especially engine related?

 

Sounds like the system wanted to make sure the engine was warmed up before putting a load on it, and didn't have the energy in the battery to keep the speed up during that time. Kind of hard to say from a one time event that could simply have happened from a rare computer glitch.

Anything else that seems out of the ordinary, like reduction in efficiency?

I wouldn't worry unless it happens again.

Well past due for spark plugs if they haven't been done. Coolant and transmission fluid should have been changed in that time too.

Not sure how that would relate to the engine making power but it not getting through the transmission. If there is a serious issue, I'd think it lies with M/G1, as that is what makes the transaxle work like a CVT.

 

Sounds like the engine wasn't very quick to start. My Gen 1 needed some engine TLC too around the same mileage.

A Prius with a balky engine can be kind of a pain. A conventional car, if you're cranking the engine and it doesn't catch right away, well, at least you're in your driveway.

A Prius puts up the READY light and off you go on electric, and then the engine kind of sputters to life eventually, or it doesn't, and drops you on the side of the road five blocks from home.

 

Cranking a car engine on your driveway for 30 sec. is kinda normal; but moving 60 mph down the highway - must've felt like an eternity.

Have you been able to do an OBD scan for trouble codes? There's probably a P300, intermittent miss or P30x - x = cylinder number misfiling.

You should be on your second set of spark plugs, your transmission fluid and fuel filter, should've been changed. If those haven't been done start there. Absent trouble codes, ignition coils and intake manifold cleaning would be next. I'm making an assumption that the problem is due to deferred maintenance, rather than something actually broken. I'm also amusing engine -oil and -air filters are being changed on schedule. Everything listed above will cause intermittent issues.

Get back to us with the trouble codes and we can narrow down the fix further; rather than taking a stab in the dark.

 

So this is dealer maintained; they're usually pretty good at doing basic maintenance work - just don't let them talk you into any expensive fixes for now!
I have read reports, on very rare occasions the CPU would miss the "hand-off" to the ICE, which will cause a delayed startup. Like what you experienced. Unfortunately software hiccups and glitch are now the norm. Ask the dealer service department if your on the latest software and that you've got all the latest patches installed. This shouldn't cost you anything, since you've been such a loyal customer. That may resolve your issue.

Good Luck......