[quote]...and the other (vent?) goes into some plactic deal. There is a wire harness going to it and some vacuum lines...if I unplug the wire connection, nothing seems to change (no check engine lite, or anything), the motor runs fine. Does anyone know what this could be, and if it could be the problem?<hr></blockquote>
That is the purge cannister on the EVAPS system. It returns excessive fuel vapors to the tank/or reburn at selected times. It can lead to the symptoms you describe if it hasn't been maintained.
What year is the car?
You really need to get the factory shop manual for the car as they have diagnostic routines to cover about any malady that you might come across. You need to be able to access the codes (if any-and you don't need a scanner) and check fuel presure/delivery.