gts-t air or fuel problems

just wondering what the third gas line is coming out of the tank?
right after the axle it goes into what looks to be a mini filter.Does anyone know if it is a filter,or what it is?
The reason I ask is because my car keeps sputtering when I accelerate hard from low rpms. I switched my motor out a while ago,the only thing i didnt change so far is the mass air flow sensor and the fuel lines.The old motor did the same thing also so i doubt it has anything to do with the electrical or mechanical aspects of the new motor.

thanks,
Garret

It is probably the vent line.

Vent line. Goes to charcoal can on stock USDM car’s. Never really looked at JDM’s with it. Unless you want to pass smog you don’t really need it. As since we live in Alberta pull that shit out and add lead to your gas. All the cool people do it

yeah i pulled the charcoal canister out already.but would that little filter thingy in the lines make my car sputter n shit?
cuz im thinking its the maf now,the car runs not too bad in hotter weather.
as soon as it gets cold air in it it doesnt go past 3000 without sputtering and bitching.