2001 Saturn SW1 service engine light

Hi, My service engine light has been on for a few months now. The only code I got was for misfire so I bought new spark plugs and wires. Now there are no codes but the light is still on. We reset it and it stayed out for a few minutes while the car idled. Its sounded great, high fives all around, and then it chugged for just a split second and the light came on again. I drove it for a while and the light sometimes blinks when I get to around 45 mph and then stays on after gear shift. I also had my cigarette lighter die out and had to keep replacing fuses for that? I have a slow oil leak on the top so I put in for a new gasket for that as well. Its got 249734 miles on it. I notice also that when I drive for a while and put it in to park it idles up so high it sounds like it gonna blow up so I quick shut it off. Once I turn it of and turn it over again its fine. Really weird. Hmmmm. I also am having the oil changed tomorrow too. I was told sometimes these Saturns are finicky and it could be as simple as an oil change is needed. Is that true? I have to take it thru inspection like 2 weeks ago lol but I know they will just fail me so Im trying to fix it. Im on SSI so my finances are very low. Plz help. Thanks so much for your time. Jen