Vague Steering, Subtle Shake

My wife has a 2008 Prius with ~120K miles. I don't drive it often (I'm a biker) but I've noticed a disconcerting thing recently that feels like an expensive repair job lurking just around the corner...

I first noticed it coasting downhill on a wet freeway at 40-50mph: the steering felt vague with little feedback, sort of like sliding on smooth ice. It didn't match the conditions (I wasn't actually sliding) and I couldn't think of any reason for it, so I pulled off thinking maybe the wheels were loose (I'd just switched from snow tires back to regular).

The lug nuts were fine, but thereafter, I often get the feeling that the steering is vague or that cranking around on a turn will break something and send me careening.

One other thing: there's a very subtle shake sometimes while rolling. It seems to be just at the edges of neutral steering, as you go from just left turn pressure to just right turn (and maybe the "straight" wheel position between them is a little wider than I'm used to). I've also noticed more shake/vibration when the ICE turns on.

My guesses are:
* Engine mount?
* Steering (rack & pinion? CV? Shock tower loose?)
* Alignment?

But I don't really know, and the effects are so subtle, I'm not sure a mechanic will even pick them up.

Is there anywhere I can look to narrow it down? Should I just wait until whatever it is breaks?

Thanks!

 

I don't think so...we're original owners, and do recalls pretty soon when we get the letter, but I don't remember one about steering. I'll give the dealer a call next week to check.

 

The Toyota recall-by-VIN site doesn't list anything open, but maybe the dealer will have more accurate information.

 

re: Tires: Kumho Sense, standard size, 35psi all around, near end of life but not bald.

I'll take it by an alignment shop to have a look...that sounds like a reasonable possibility.

Thanks!

 

Dropped by the dealer and had it checked...they said the tech saw the steering problem, but no alignment, motor mount or other problems. They thought it was just uneven tire wear. So, since the tires were going to need replacement soon anyway, I had them swapped today. Much better, no more shuddering. I'm hoping that I'll even get better mileage with Yokohama Avid Ascend LRR tires than I'd been seeing with Kumho Sense.