when accelerating car revs high and then returns to normal

about two weeks ago i noticed my car started having trouble when I idle it starts to shake as if its going to stall out then when i start to drive it it returns to normal. took it to a mechanic and said my fuel injectors were clogged bad and i had a very dirty air filter that he had replaced. It was driving fine for about 3 days then the same issue proceeds to happen except now when i step on the gas lightly my car stutters then shoots up rpms and when i let go the rpm decreases rapidly almost instantly. Sometimes when I idle it shakes shakes i usually see it about the 500 rpm mark and to which it causes my car to stall and then i have to turn the key and step on the gas to get it to turn over and able to move again.