2007 Toyota Yaris Hatchback - Steering wanders

Steering problem
2007 Toyota Yaris Hatchback4 cyl Two Wheel Drive Manual 65000 Km

Hey guys,

Having some trouble with my Toyota Yaris, figured someone here might be able to give me some pointers.

A little over a month ago, I started to get a wandering feeling from my front end. Though I can feel the difference in my steering slightly at lower speeds, this becomes a real problem for me at highway speeds as the car no longer feels stable when going around bends in the highway, or if a little wind pushes on the car.

I have been driving this car for about a year and while it is a light car and at times it can be affected by wind, I'm absolutely sure it does not feel the same as before. I have taken the car in to my dealer 3 times now and they were unable to identify that there was a problem let alone fix it. I have replaced my tires (as they were bald anyways), with this replacement they realigned and rebalanced the wheels. Then they rebalanced and aligned them again after I complained I was still having trouble. They said they have checked "everything" and it is all tight and functioning the way it should. I then took it to another garage (not Toyota), and while the person was able to feel the wandering feeling when we took it to a test drive on the highway, they were unable to figure out what was wrong with it either. They told me they can try and replace certain parts to see if that helps, but I don't have the money to be spending on parts that may not even be broken.

The wandering feeling I get is not consistent and only shows up unexpectedly, being more pronounced and more frequent at higher speeds. It also wanders both ways and doesn't appear to have a preference one way or the other.

I have been told that this may be normal and caused by the type of power steering the Yaris uses, but I don't see how that can be the case being as I have driven it for a year without any such problems until now. I was also told this may be due to the anti sway bar but I'm not a mechanic and I'm not sure if that could be the case or even if my car have one.

Some more details:
- The problems gets worse the more people are in the car.
- At times it feels like the steering wheel sticks and at other times, it feels too loose.
- The problem becomes much more noticeable, and it becomes very difficult to maintain a straight course when driving on a stripped road (when the road is under construction)

This problem has been driving me insane for well over a month now, I would really appreciate any input from anyone regarding this problem.

Thank you for your time in advance!