Miss fire code 302 and 147

Emergency lite flashing, car runs rough at idle, and at speeds up to around 40 mph, when on highway, at high speeds rides a little better, I changed spark plugs and wires, destibuter cap, rotor button, ignition coil, fuil filter, sprayed throttle body, sprayed around intake for valccum leak, put in sea foam, car still runnig the same.