My Aviator exhibits this behavior after it's been somewhere the steering system has to work, like a canyon. The steering effort goes up while the sensitivity to the inputs also increases. So at Freeway speed, the steering effort is really high and it's impossible to correct a drift to one side or the other. It goes to one side lane, you try to correct it and it's too much, it heads across the lane, crosses the line, the lane minder pops up on the HUD say the lane keeping has been cancelled as it goes across the other paint stripes. You cannot keep it in the middle of the lane. I took it to the dealer and let the service advisor drive it, it didn't do it. Couple of days later I took it out on the Freeway in the morning and it wouldn't do it then either.
It did it twice while I was driving it home to Utah from Colorado, mountains most of the way. The first day was about 300 miles and it did it for about the last 50 miles which were basically flat. Second day was about 400 miles and the last 100 miles going mostly down hill, on a Freeway, was a really pain in the you know where.
If you have to get the steering system hot before it'll act up, I'm not sure how we'll ever get it fixed. The issue is addressed on page 309 of the owner's manual.
