Probably the cannister is full, not being flushed properly. 3 lines to it, the P line on top goes to the P port on the throttle body (P=Purge). The other line on top goes to the fuel tank vent and the bottom line is just run down to the frame rail to atmosphere:
http://www.4crawler.com/4x4/CheapTricks/22RE_Engine_Pix/19.html
The FSM has the testing an cleaning instructions.