Sounds like a throttle problem, this is how i understand it.
remember there isnt any throttle cable its early drive by wire system so the accelerator is basically an electrical button connected to a switch in the engine.
If some of that system is out of adjustment and the switch in the engine gets a signal it will accelerate. my 2001 GS300 doesnt do that but it is very sensative in the accelerator and sometime in the city I will hold it a second on the brake because as soon as i touch the accelorator it takes off