2004 MAZDA MPV User Comment / Complaint

I purchased a 2004 mpv arch 28, 2005. to date, i have had this van in for warranty service to replace ignition coils three times: 10/31/06 ¿¿ 31,770mi - #4 coil replaced. transmission range sensor replaced also 12/05/06 ¿¿ 33,229mi - #4 coil replaced again 1/08/07 ¿¿ 34,708mi - #6 coil replaced. today as i was driving, the same symptoms ¿¿ steering wheel vibration, bucking, lurching ¿¿ occurred as before when the other coils failed. the cel came on, i checked for the code and i discovered that the #5 coil has failed. now this will be the fourth service for the same problem. there has been no effort on the part of country mazda to find the source of the coil failure. replacing the parts obviously is not solving the problem.