I have an 04 Land Rover discover, 4.6. I am continuing getting miss fire codes such as P0300, P0303, P0305 P0306. Keep getting the code suggesting a Idle Air Control valve, which I have replaced. I am not getting codes, P1171 and P1174, which suggest the air fuel mixture is off. Can someone please help me figure out what is going one with this thing. I have worked on this Rover for over a year trying to get the bugs worked out of it and I am getting pissed.