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Lost & confused

i have a 04 grand caravan 3.8 liter. after filling up with gas & only after filling up i have a prob with the way the van runs. it will start and idle fine but once i shift in to gear and try to drive it starts to buck. if i take my foot off the gas it wants to stall. if i shift in to N or park the RPMs are around 400/500. if i rev the motor in N or park it will smooth out and idle fine and drive fine until the next fill up, then it starts all over again. i am lost & confused can you help???

Do you ‘top off’ the tank when you fill up (put more gas in after the first click)? It sounds like you have a problem with your evaporative control system. Try putting in about a half tank the next few times you get gas, then fill only to the first click, see if that helps clear out any gasoline that’s been forced into the evap system.