It'* not hard to do, but it can be a pain to track down exactly where the problem is. It could be the control solenoid, the vent valve, evap cannister, fuel tank pressure sensor or any of the lines running between the different sections. Start with the lines for a vacuum link as Bill suggested. Start by the control solenoid, the small black cylinder about in the middle of the engine back by the firewall. You'll have to remove the engine cover to see it well. Check the lines there, also at the evap cannister under the car near the about under where the rear seat is, as well as the lines running to the vent valve by the back tire.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.