2000 polo gti's aint slow in any case and there 125hp standard. if it sounded rather grunty then its got an induction kit which they respond well to (132hp my mates one) anyway back to your car, check fr any leaks at the bottom of the cat after it was gutted as this makes your car uber slow (i found that out the hard way) and makes it sound rough. also if u aren't running any other mods, i'd bypass the LO boost solenoid i think mines is overfueling aswell tho lol, after my glanza's bn allowed to 'stretch its legs' i get a nice big wiff o optimax lol, not too bothered about it cause it mean