You don't say what model of Janome you have. I had a similiar problem with my 8900 but upon checking the Accufed walking foot, I noticed that the back of the foot that attaches to the back of the needle bar had slipped out of place. I think this can happen when I try to stitch at the fastest speed. I have a Babylock walking foot and the instructions that came with that foot said to sew at medium speed, not too fast. I have much better stitch if I don't exceed the medium speed.