Doesn't understand

I need some clarity on certain issues regarding Toyota. I bought a Etios Sprint September 2017. I haven't had any issues with the car, then suddenly when i stop at a stop street the car over revs and then goes back to normal. I took the car to Algoa Toyota and they said they cleaned the throttle body. It was much better after that, but now the car under reved/dipped when idling. I took the car to Algoa Toyota today for the following: Under reving Check suspension Front window fog.

Everything was sorted to my satisfaction and i have absolutely no complaints regarding Algoa Toyota, but i am not satisfied with the answers i received. I asked the service consultant why this is happening and his answer is that this is unfortunately one of the problems of the Etios Sprint. He then went on to give me examples of other vehicles and their faults etc. The problem i have is that how is it possible that a new car from a very reputable company "is just like this"? There is no way i am happy with this situation and i want to find out from Toyota as a company if this is true? Does the Etios sprint have these issues and if it does what is Toyota doing about this? My other question to the gentleman was that what am i going to do when my warranty expires? He then said it will still be looked at and i wont be charged for it. Again, is this true and if it is can i get something on black and white?