1994 Grand Am Gt 3.1 Running Rough

Hi, I have a 1994 Grand Am Gt with a 3.1 and 215,000 miles. The car has always run pretty well until recently, when it started to idle rough. The whole car shakes when at a light or sitting in park. If it is warmed up, it doesn't shake so bad when in neutral. It is louder than it ever was too. The sound does not seem to be exhaust either, especially since I just had that replaced about a year ago. Also, the noise seems to pulse as I accelerate. Within the last year, I have replaced the fuel filter, the spark plugs and wires, the water pump, the radiator, and the heater core. Any help would be greatly appreciated. It feels like a completely different car when I drive it and I can't stand it.