2000 rodeo timing? help!

Hello, I have a 2000 isuzu rodeo 2.2 4cyl 95,000miles manual trans. Ok my starter went out and I did not have the dough to replace it, so I have been kick starting it using the clutch. the car ran great and now I have oil in my #4 spark plug, decreased engine power, and my computer keeps reading misfire. when in first I have to rev it to about 2k rpm to keep it from stalling when I let the clutch out, and at 3k rpm it gets a shot of power. when you rev it from idle position giving it a straight shot of gas the engine will rock from driver to pass side in the engine bay, but if you slowly give it gas it will rev out perfect! at idle it runs just fine. is my timing messed up? someone said that I needed to change my valve cover gasket and I have that part ordered and on its way , I will be replacing it as soon as I get it. I need to know if I need to take it somewhere and have the timing adjusted. I think the belt was replaced because there is a sticker on the top of the motor that says it was, but all the writing is worn off, so I dont know when.
Thanks!