Car runs like shit

Let me tell you about My nephews Saturn same model as yours. It was bucking ,popping, bogging they (My brother too) checked everything vacuum, timing, full tune up ect still not fixed nothing changed for the better so they reluctantly to it to a shop they said it needs this (don't remember) but did not fix it and they looked & looked and never could fix it and a couple weeks went by so they towed it to a school that teaches student to repaier cars and they did every possible thing including taking the engine apart putting it all back together found nothing wrong so it must be a ECM and they put 3 on it and none solved the issue, So my brother said this is gotta stop and called the school up and said Halt stop until I get back to you, he looked around for a wrecked Saturn bought one and took it to them they pulled both and put the wrecked cars engine in and it ran fine. Job Done. So I can tell you in advanced I have no clue and neither does anybody else My brother talked to folks local and all over the country trying to figure that thing out. I was in the hospital for a year and did not touch it so I may have been able to figure it out but can say find another engine unless you have months to figure it out, my brother knows his way around any car.

Let me add he put a computer in it too before taking it to the shop the first time.