2000 Chevy S-10 running rough doesn't make sense

I have a 2000 chevy s-10 that runs rough, like it's missing, it's been running like this for about a day. I have new plugs and wires etc. I drove it to work and it started running with a hard miss, hesitation, stuttering, loss of power. I made it to work, was driving it home and it was continuing the said problem until suddenly correcting itself and running fine. I got in it to come to work again and it's missing bad again, service engine soon etc. What could be wrong and why would it correct itself and go back to running bad again?