I agree, pop into the city for a good Italian meal. Two of my favorites:

1) You won't find a tourist here:
You can take the train from FCO to Ostiense station, then subway line B to Garbatella. There is an amazing hole in the wall restaurant for an experienced traveler only called Ar Grottino der Traslocatore (Largo Delle Sette Chiese 2, 00145 Roma. Tel 06 514 1261). Incredible home-made 'cucino romano' cuisine. Call to see if they're open for the time you want though.

2) For pizza:
You can't go wrong. My favorite is a trendy place on Via del Vantaggio, a small street near Piazza del Popolo (subway stop Flaminio), but I forgot the name. Then you can walk over to the Spanish steps before returning.