I have driven 2 generation FL VIOS for 3 years and the realized the juddering and jerking or refer to slower response from the dbw, wasn't felt much delay from the system but instead more likely from the weird 4 speed gearbox, may be the gear ratio or something like that. At first i also though the dbw throttle system sucks, but after that, i shifted to current ride, an Prius hybrid, definitely having the dbw system for throttle. While on power mode, the throttle response very fast, almost instant, or at least i can't feel the obvious delay, may be need to use diagnostic tool to check, in order to find out if the throttle response is delayed or not.