93 euro stalling

ive got a 3.1 1993 lumina and it usually runs great...now its been stalling in driveway when it is idling...i go out and it starts right back up and runs good....it stalls in town like when slowin down or turning a corner..and it some times hesitates goin down highway..only for a second like it acts like its gonna quit then just takes right off and runs great....any help would be great...when it quits it always starts right back up..i did the jumper for codes and just came up 12 ..what is a 12 code?..engine light is not on ..thks