During a test drive of a 1990 535i automatic with 109k miles today, everything was fine except for two things. One, at higher speeds the rear end seemed to "skate" a bit causing the car to be a bit twitchy - undoubtedly becasue of worn out rear subframe bushings. Second, after driving on the freeway and coming back down to city speeds, the throttle seemed to stick. When put in neutral, the revs were around 3000rpm. After the car was put back into drive, the throttle and idle were normal for the rest of the drive. Is this a reason for concern? A common problem?