This exact thing has not happened to me but something similar on my Janome Magnolia 7330 machine. About 3 months after I bought it I was sewing & let up on the foot pedal & it kept sewing. It would not stop. I had to unplug my foot pedal to get it to stop. Then, out of the clear blue it would start sewing when I wasn't even sitting at the machine. I took it in to the repair shop & was explaining what was going on to the repair man & low & behold .... it started sewing as we were talking & just looking at the machine. He checked it all out for me & replaced the foot pedal (it was still under warranty so Janome paid for the service call & foot pedal). That solved my problem.