wobble at 55 mph?

I'm not quite sure what you mean the car sways back and forth. Is it the RPM going up and down or does the car actually rock back and forth? When you set the cruise control the RPM will go up and down trying to maintain the car's speed.

 

What you are probably feeling and are not use to is the CVT. The CVT keeps the engine running at an RPM that is higher than you would normally get with a regular automatic transmission. The CVT and the computer keep the engine in its optimum RPM range for fuel efficiency.

 

I drove Prius for the first time today from dealership - 150 miles. I noticed that, to. It feels like if you would drive regular car and kind of press the gas pedal to go faster but immediatelly release it again.

I noticed that when battery is almost full, occasionally the power from battery is released by engaging the motors to help the engine even at higher speeds when just cruising. Perhaps it is related?

 

I suspect you may have a problem somewhere in the running gear. I suggest that you try to have the Prius Tech at your dealership ride with you, or drive it him/herself in an attempt to duplicate the symptoms with you in the car

I often have run my '05 within that speed range with and without cruise control engaged and have not noticed any "wobble". By that I mean I have neither heard nor felt engine or transmission surging. Nor have I experienced any speed fluctuations. Occasionally on the interstate I will experience cross winds that make the car feel as if it is lunging side to side or fore and aft. This is especially true with semis in the next lane at a speed different than mine.

One thing I did notice this evening that was a bit unnerving. It had been raining moderately and was still raining slightly. The wind was gusting across the highway, and it felt as if the car was skittering sideways when a gust would hit. I still have the OEM Goodyear Integrity tires and have read many negative comments about them, so I suspect they were a major factor in the instability. Is it possible that you may be experiencing symptoms where the tires are playing a part?

 

Did you go over any curbs or skim curbs?
Your tires could be off-balance.

 

The Prius weighs less than 3000 pounds, is rather narrow, tall, and has a large side surface area. A strong sidewind can push the car and make you feel that it's sliding sideways. I doubt that different tires will be able to off set these design elements.

The original tires seem fine. My tires have 13,000 miles on them and it looks like they'll easily be good for 40,000 miles.

 

Also be careful about pot-holes! They can cause your alignment to go off a bit.

 

I have to say I have nothing like you describe. I would guess that this is a problem specific to the car you drove?

 

Wish I could shed some light on your problem but we have had our 2005 Prius for two months and have driven over mountain highways at 60mph in rain slick conditions with 25-30 crosswinds without undue concern. Yes, the gusts keep you on your toes regarding steering ( toes/steering?) but has not been a problem that I haven't had in varying degrees with any of the cars I've had in the past 50 odd(?) years. Think a trip to your dealer to check things out would be your best bet.

 

No wobble here.

However, it is normal for the energy flow diagram to show energy going in and out of the battery, back and forth, back and forth. This should not affect the actual speed of the car. If it annoys you, turn off the MFD. It's just the HSD doing what it's supposed to do.