Truck spits and sputters.?

I have A '98 Ford F-150 Super Cab 4.6 V8. I just got it 3 weeks ago. The engine light flashes for a little while then stays on. If i give it a little gas it starts to shake and spit and sputters, but if I give it alot of gas or idle I have no problems. Im thinking its the plugs and/or wires. Is their something else i need to worry about?