Evap/fuel tank pressure control system malfunction. Easiest thing to check is to make sure you have the proper gas cap on the car. Some info and links for you here for the evap canister system, in case the gas cap is not the culprit. By the way, the check engine light is not an idiot light. When the CEL goes on, you should attend to it, as the computer is trying to communicate with you.
'91 Tracker 8V, 1.6L, 5 sp, 4wd, 2dr, conv, CAMI, 'slightly' rusty
'97 Suzuki Vitara 8v, 1.6L 5 sp, 4wd, 2dr, tintop, horribly purple
'61 NSU Quickly - 150mpg