It sputters until I can find the sweet spot in the pedal and when it finally gets to speed its good. But when I come to a stop then it does the same sputtering. If I give it too much gas it sounds as if its backfiring near the catalytic converter. I've changed my timing belt plugs/wires. My friend has the same problem with his 1998 expedition. He's changed the coil pack and O2 sensor with no luck. We need help!