sr20alex

Well yesterday i went to go change my oil at a local place. As soon as i changed my oil the car started to act unusal the car idle bounced up to 2.5k then droped down to 500 then went back to 1k then my seatbelt light didnt go off even though i was wearing it then later it went off. Then my engine light went on for like 5 minutes then the light went off so i start to worry. Then today i was launched my car for fun at 3k.. 5 minutes later the engine light went on so i thought okay it'll turn off later and it didnt then when i was doing a turn my car all of a sudden just shut off. I pulled to the side pop the hood and started the car started fine then a it stalled again. I check the for anything loose but there was none. Anyone know what could be wrong?

info on car
1991 240sx hatch bone stock no modifcations to it whatso ever

sorry if it was long.
and thanks!