I have an 04 Mazda 6s ATX, 3.0l engine, 118,012 miles and have been experiencing a 30-50 mph shutter as if it is misfiring, but no misfire code. Took it to dealer and was told it needed a new tranny, didn't believe them so I took it to a reputable transmission shop and was told that the tranny is fine it is the engine misfiring. I changed the plugs and it drove smoothly for a day then back to the jerking. I then changed out the coil packs and same thing, good for a day then back to it's old self. I should add that I still didn't get a misfire code before the above replacements. Next I took it to a shop and had them do a vacuum leak test which showed a leak at the EGR valve, had it replaced and again, good for a day then jerking again. Not sure what to do next, had some thoughts about the ATX speed sensor or the shift solenoids. Any ideas?? Hate to get rid of this as everything else is great and my daughter loves driving it otherwise.
