2002 Saturn L100 Engine sputters when idles

My 2002 Saturn L100 recently began to idle and drive rough. The Rpm's would drop and the engine would begin to cut out but as you began to get going again it would be fine. The service engine light came on and I took it into a local shop. They gave the car a tune-up, fuel system cleaning, changed the oil, oil and fuel filters. It seemed to be running fine, but a day later the problem returned, not as bad unless you run the AC. I have read posts about vaccumm hoses, replacing radiator caps etc. But I am not sure what I need to do. I am hoping that it is something simple that I can repair myself as funds are really short after the last repair bill! Or at least go in knowing how much something like this would cost to fix.

Thanks so much.

Steve