Engine doesn't want to shut off sometimes

My mistake: Dr Prius.

 

when that happened to me, an italian tune up took care of it. but i think it might have been egr circuit clogging

 

it might be a possibility. normally, you're good for 100-150,000 in most cases i think.
but the very low mileage may mean a lot of warm up time, and not much steady driving at temp.
but it's just a guess.
i had trouble at 87k, i think because it was a plug in, and the engine often ran just for a minute or two, not completing the warm up cycle.
i never confirmed the egr, but had all the symptoms and traded it in.

 

It's so easy... You just have to change the clock back to the correct time... An also any pre-sets you want on the stereo. For the window, rolling it all the way down and then all the way up to set the auto roll down function.

 

i don't think i was clear. it's not when you get the symptom, it's what's causing the symptom. but idk if it's the egr circuit or not.
there are four tiny ports in the intake manifold that clog

 

A stuck open egr will make it stumble or stall at low rpms. A clogged egr will do nothing at low rpms. It is designed to be closed at those times.

 

I would do an EGR cleaning by 50k, and every 50k thereafter. That will keep it more-or-less functioning as it should, moderating engine temps, and keeping them uniform across the cylinders.

@bisco's correct that you'll likely be "good" till 100~150k, but "good" means the engine's head gasket will survive till somewhere around there, before the ever-more-clogged EGR system causes it's failure.

 

the engine not shutting off thing is puzzling. i couldn't understand why it was happening on mine, or why the italian tune up fixed it.
i could only think it blew some gunk out somewhere

 

About the only thing running the car at maximum rpms for a period of time might do is dislodge some gunk on the throttle body. Cleaning the throttle body is easy as long as you can remove the air intake box and carefully use specific throttle body cleaner.