98 Corolla starting problem

194000k, 98 corolla ce.

I have a new starter and charcoal canister. Car starts fin cold. If its been running a while it may need to turns of the key to start. But the killer is every time I stop to get gas it takes 5-10 minutes to start. And when it does start it idles ridiculously low and shakes a lot, until the rpm's slowly increase. It does this EVERY TIME! The gas cap has be checked and it even runs with no gas cap. The mechanic at my local toyota figured it was the charcoal canister and over $600 later (the next day) its still the same. Any info would be appreciated, thanks.