Just put some new brisk lgs plugs in my M6 and the car wants to sputter out when i take off and the revs drop below 1000. Also when i punch the throttle below 1500 it wants to sputter. My first thought was that i didnt connect all the wires but i checked and double checked, no prob there. Car feels alot stronger up top so i wouldnt think a bad wire, because it would miss in any rev range. What might cuase this miss.TIA.