Inexplicable Gas Mileage Drop

Any of those done badly might have created your problem. Unless they can show you a problem code associated with the PCV valve all of those things were done to flush out your wallet. Only the regular maintenance items on the *Toyota* checklist (not a dealer's checklist!) are required. If you don't have the Scheduled Maintenance Guide see here:
Toyota Parts and Service

See also posts by Patrick Wong and Galaxee for a few other valid infrequently-done things.

 

I have EXACTLY same symptom as you. slowing down going down a hill (like the break is on) no glide. major fuel economy drop. I am due for a service next month, so I am going to be asking similar questions. I hope you work it out, if I do I'l post it.

Cheers

 

I had a very similar problem just recently after having the oil/filter changed. The oil is NOT supposed to be all the way to the upper dot. The dealer had filled the oil to very slightly over upper dot. It should not be more than 3/4 of the way to the upper dot. I drained some oil ~1/4 quart out and now my Prius again glides and MPG is back to 48.5. When the oil level is too high the engine labors as it increases internal drag. The regen and coasting are reduced due to the increased internal engine drag.

 

Very unlikely

At speeds below 43 MPH the engine doesn't even rotate during regen.

At speeds above 43 MPH the engine does rotate, and if the oil drag is higher then very slightly more fuel will be injected to keep the engine rotating, but no increased drag will be noticed during coasting.

 

Oops - sorry. Wrong forum. I thought this was for the Gen III.

Here is my post anyway (since I cannot delete it).

This winter I used Blizzak snow tires, installed on steel rims. When I installed them in November, I could notice a clear drop in gliding efficiency. On the same hills as usual, I could feel clear resistance when trying to glide. I interpreted that as
1- tire adherence (blizzak are designed to stick to the road).
2- wheel inertia (steel wheel are heavier, resisting acceleration more.

I got my summer tires back on for a week now, with the standard rims (that came with the Prius). Gliding is back to normal now!

 

You'll get the same feeling when installing 17"-19" wheels too.