1994 Saturn SL1 missfire / stall

I purchased the car last summer everything has been great on it. Up until yesterday. I replaced the spark plugs and wire to see if that would help but it did not. Some time when now when I start the car it take longer then normal for it to start up. And when it idl now it seam like it want to die it will be at 1500 rpm. And then drop to below 1000 and then it will pick back up. And then when we are driving down the road it seam to miss fire the engine. It only seam to miss fire when we are at freeway speeds.