Service engine soon light keeps coming on...

Having yet more problems with my 1999 Alero.... that's a shock, huh?
About a month ago, I had noticed the car had a rough idle when parked or at a stop sign and I could feel a miss when driving; usually began at around 45 m.p.h.
I had new plugs and fuel filter put in but that didn't solve the problem. Now the service engine soon light comes on. Still have the rought idle and missing. The light will stay on for a little while then go off. It's back on now.
Any ideas?

Go to Autozone and have the code read. They do it for free. Which engine do you have? That would help in finding the problem.

or u could have the manifold cleaned my wifes car had the same problem and we cleaned the manifold well not us the shop itll cost around 200 to 250 to do this by the way how many miles u have on her and you might want to try throwing in a bottle of fuel injector cleaner in her my wife had a 94 old cutlas and we have 250000 miles on the car we do this oh every 75000 or 100000 miles it cleans the intake out and u will have more power like brand new or u can replace it at over 500