2003 Chevy Malibu rough idle

According to my fiancee, starting today, car is having vibrations/shudders more pronounced when idling, but also slightly noticeable while driving/accelerating. Apparently also has a new idling sound, and initially the check engine light was flashing, but now is solidly on. I know this is relatively vague, but any thoughts? Thanks.

When the CE light flashes, you have a bad misfire....