What could cause a 20 valve to just suddenly start to idle poorly and cut off all the time? You have to hold the brakes and press the gas a lil so it doh cut off when driving

When it idling by itself, it at like 2-300rpm. If you hold the rpms till 900 or 1100, it sounding like it have aftermarket cams
Anyone? Plugs?, Gas Filter?, Plug Wires?, Air Leak?, Airflow?
Also inside the car, when you driving and let off the gas, you hearing air releasing like it inside the car.
