i've had this problem for about a year now but i'm in the army so i haven't been able to fix it due to training. when i take off it's almost like there's not enough fuel or air getting to the engine. it's kinda hesitating a bit, nothing crazy bad though. i did some work on it today, replaced the IAC and changed my plugs. this semi fixed the problem, it's not doing it nearly as bad as it was but there's still the slightness of it. now the reason i'm really postin this is that i think it might have something to do with my gas tank. why i say this is because the part that goes from the fill up point (dunno what to call it) to the actual tank itself has a problem with the seal. so when i fill it up completely is leaks until it levels off there. i'm wondering if this would cause my tank to not pressurize right and make the fuel have a hard time getting pumped to the engine.

 

if your tank has the same leak mine did the grommet around the fill tube to the tank is deteriorated and is leaking thats an easy fix took me about 30 minutes once i figured out what i was doing. not sure if this would cause ur hesitation, it didnt effect my car at all have you tried cleaning the MAF or maybe dirty injectors?

 

the filler neck has nothing to due with pressurization, however I would fix that just for an obvious safety concern. the system basically works like this, you have a pump in the tank that sucks gas into the line, through a filter, then into the fuel rails where the injectors then feed it into the motor. From the fuel rail there is a relief valve on it that regulates the pressure by opening and closing returning excess fuel back to the tank to restart the cycle. the tank is never pressurized, it is in fact vented to prevent fumes building up, or even causing a vacuum preventing fuel from entering the pump. I think your problem may lie in the filter. it would be restricting flow and not causing pressure to build as fast as it should. when is the last time you changed it and how old is the car? Also is it a stick? if it is you may be letting the clutch out a tad to fast which would cause the same symptoms.