Whenever i let off the gas, or push back on it, in lower gears (it happens in higher gears too but not nearly as noticable) my car jerks. if i let off or push the gas in VERY easilly it does not do this. if i quickly let off the gas or press on it on the other hand, it just "bucks" pretty hard. any ideas? i was told to clean the throttle body and check the motor mounts for stiffness.