hi guys i'm new here and new to vw's so thank you for any help you can give me

my recently purchased passat is running like sh** all of a sudden, it kind of feels like its running on 4 cylinders, rough idling, loss of power, almost wants to stall

no warning lights on the dash or any warnings on the display

does anyone have any ideas? its been great for 3 weeks it ran sweet

p.s after alot of researching already i have changed the famous problamatic black top coolant sensor to the updated green top one but its not made any difference i cant seem to find any info on passat v5's, are they rare ?