2005 Volkswagen Polo car has a lack of power constantly stutters in the 1900-2400 rpm range and feels like it will stall anytime from gear 1

Have a serious lack of power and have to overuse gears to build speed used to able to hit 110MPH cries now at 80MPH
Have had the engine light come on a couple times but comes as quickly as it goes
I know that my belt is a bit tight and that's why it whispers
But the rattle sound defiantly comes from using the throttle