Likely a dirty throttle body and dirty/clogged up intake manifold and intake valves.
The throttle body can be cleaned easily by taking it of and use carb cleaner and soft brush. Disconnect the battery. Don't put any forge on the valve it self well cleaning and spray it clean.
After reinstall only turn on the ignition but don't start the engine and untill the buzzing/beeping noise from the throttle body stops. Then afterwards you can start up the engine.
Concerning the inlet valves, they need to cleaned using the walnut blasting methode.
Removing oil deposits from the intercoolers and piping revamps the engine running behaviour certainly.
Good luck.
