if had faced the same issues, for the car turning off at low acceleration as per mechanic the slow jets of carb and the pump of carb were not working properly & carb m petrol over ho rha tha,, , once this issue was catered then the issue was resolved ,,, for the hissing sound, i had the sound constant , not only at acceleration but also at idle condition,,, mechanic blocked the pcv valve pipe with polyethene and the sound was gone,,, this means k pcv valve ko bnd kr dya ,,, i tried couple of diff mechanics but all did the same method , even though i had a new japense pcv valve but still the issue was there and eventually had to block the pipe,,, i am still trying to get a proper solution to it so that my car pcv valve is active again but yet no success