I have a 99 gs400 that had this problem about a hundred and twenty thousand miles ago. I took it into a local mechanic who told me that the left lower ball joint was bad. He replaced both lower ball joints and the problem immediately went away. Shortly after the problem resurfaced and we determined the ball joint was faulty. We replaced the faulty ball joint and the problem again went away. It is now back at two hundred eighty five thousand miles and I can find nobody to tell me what's wrong with the car so I'm going to tell my mechanic to replace both lower ball joints. It has to be the problem because it is identical to what the symptoms were the first time around. It's just odd that I'm telling the mechanic what to do.
