Prius Needs Premium Gas?

 We got a Prius about a month ago, and so far it seems like the car is
happier with premium gas.  With low-octane gas, when the gas engine shuts
off, it doesn't do so smoothly - it kind of "ka-chugs" a couple of times
before stopping.  Is this normal?

Thanks!
Chris

 

Mine does that sometimes when it is cold.  I understand this is common.  I
use 87 octane and that works fine.

 Cold like the weather is cold, or like right after the car has first
started?

I am pretty sure it does this for me even after the car has been running for
a while ...

 

Mine had done this a few times in both winter and summer weather (I'm in
Minnesota) but to the best of my recollection, only when the engine was
cold.  Sometimes I think it has a conflict of interest:  It wants to shut
down because I'm not putting a load on it but it wants to keep running
because my catalytic converter hasn't warmed yet.

 

It's normal.  The engine is burning off the last little bit of gas so it
doesn't evaporate (evaporated gas being a worse pollutant than burned
gas).  Prius never needs premium; if it ever pings, it needs a repair.