This happened all of a sudden but getting the codes for misfire on these 3 cylinders. I have extra coils, have switched them out with the extras and between cylinders but its always these 3 cylinders. What is really confusing to me is that on start up, it runs very smoothly for 16 seconds and then starts to run rough and engine light starts flashing. It doesn't matter if I erase the codes or leave them, I turn it off and restart it and the engine runs smooth like it should and after 16 seconds starts running rough. Almost like the PCM is putting the engine in a limp mode or something, but I haven't been able to find anything along those lines. The only thing I've seen that makes any sense is that the knock sensor for the front head is faulty and causing it to misfire? The camshafts are welded. It has run and still starts like a new car until a week ago and now it's like the PCM is causing the front head to misfire? Any help would be appreciated.