okay so on the way to target tonight the volvo did something funny... i was driving in an alley and i was using a little gas, but everytime i would hit the gas the car would brake or seem to slow down or want to stop. then i looked, and the check engine light was on. i took my girlfriend's car to the store, but i came back home, and fired her up again just to see, and the car seemed to drive fine, but the light is still on. i did not hear any pops or snaps. the car still starts, but the light is on, and it makes me really nervous. i guess my big question is what could be the culprit? the gas cap is secure, i turn 3 clicks every time just to be safe. if there are no ideas would my 92 volvo have an onboard computer that autozone or someone could hook up to tell me? if you have some ideas and some rough estimates on repairs that would be awesome as well.

the car- 92 240gl automatic transmission. 145k miles on it.

work ive done recently- transmission fluid flush and replacement. regular oil changed every 3k. new distributor cap, and new plug wires.

the things i am planning to do soon: timing belt, general belts, engine mounts. and shocks/stuts.

thanks in advance for the advice!
ross