1998 Ford Taurus Ford Taurus 1998 Odd Sputtering?

Hi. I have a 1998 Ford Taurus SE that recently began to have a rough idle. When cranking from a cold start, the idle is rough in park or drive and will get worse if I turn on the air conditioner. After driving, the rough idle is random and intermittent. During driving, usually at lower speeds and on flatter roads, the car kind of lightly sputters during acceleration. During this "sputtering" I sometimes hear a knock or two from the driver's side. Problem has been steadily worsening for a week and a half. Starts fine other than the bad idle, and has not stalled - yet. Any ideas?