1995 Buick Century Engine seems to surge

Hey there.
I've recently bought a used '95 Buick Century, and about a week after I buy it, the engine seems to act up. I first noticed it when I was transporting four people in my car, dismissing it as a slight struggle from the weight of the passengers. What was happening was the engine, while idling, started to get very low RPMs. It felt like an easy sputter almost. This problem has gotten progressively worse, as it now stalls on occasion. The low RPMs only seem to happen when idling, and they will jump up for short periods of time, almost sounding like a surge. When I opened the hood of the car, I did notice some anti-freeze leaking near one of the cylinders. I'm not quite sure if this is serious or not. As of now, I don't drive the car. Any help on this issue would be awesome. Thanks.