2001 Volkswagen Polo possible engine problems

I have a 01 Volkswagen polo 1litre with 90.000 miles on the engine recently my car started loosing power slightly but not to much but the main thing is the car chugs/jumps when the revs hit 3 or 4 rpm but once it goes over that its fine again but happens every time its in-between 3 and 4 rpm. The check engine light has flashed for 2 or 3 seconds but the computer cant find any codes please help as I cant afford a new car or expensive repairs