What would cause my car to miss?

I have a 93 ford probe 2.0 liter automatic and i just had to change my fuel pump and fuel filter i also put new spark plugs in the car and it ran good for about 1 day or so and now its like i guess you would say missing but all i know is that its hard for it to stay running and when i go down the road the rpm bounce up and down like it is missing but then it will clear up. Does any one have any advice for me??