car hesitates while acceleration and idles poorly

My car from the last month has started to hesitate while acceleration. I have to jam the accelerator and the speed slowly climbs, it's really difficult at intersections and the traffic circle where you need the car to pick up fast. I have changed the spark plugs, cleaned the air flow filter and checked for leaks. There is no check engine light so its not an issue with the throttle position sensor. i have a mechanic who i take my car for repairs and he does not know whats the issue. he is guessing its the gear filter that needs to be changed but i have searched the internet and they don't say it anywhere, that's the cause of the issue. please help.