if you're mentioning engine noise when you press accelerator, let me tell you a few things.
in 2005+ models of vitz these two are fairly new things:
the acceleration pad is electronic i.e. it doesn't have a wire.
ecu controls car race/tuning, i.e. for example if your engine rpm drops for any reason, ecu will detect it and increase the rpm automatically, i.e. no manual race up/down. To my own experience I have noticed that ecu supports RPM to some very low level and picks it from there, never let the engine stop, but if you've got lots of carb and choked air filter, your engine may stop and you will have to restart by cranking the self.
in terms of how to accelerate your car, this is a standard way of doing so in automatic trans car + electronic accelerator + cvt.
* when in 'D' mode
1. To give acceleration press the paddle 10-25% of total paddle movement allowed
2. To maintain velocity (to maintain current speed i.e. for example if i am on 80kmph), keep pressing the paddle 10%.
so in theory, when your car is in 'D' transmission mode, only 0-25% of the paddle can be pressed. If you press your accelerator paddle more than 25% in a car which is auto + electronic accelerator, it will only create engine noise!!
* when in 'S' mode
1. To give acceleration when your car is less than 26kmph, you can press till 25% of accelerator pad
2. Once your car touches 26kmph+ (we're now in 3rd gear optimum speed), you're free to use 25-100% of your accelerator pad.
So just to summarize this all, what I have learnt is that when in normal mode ('D' gear) you really dont need to press more than 25% accelerator at once at any speed. The 25-100% accelerator paddle is for 'S' gear in these CVT cars
I hope it helps