My old Pfaff did that after it was about 15 years old. I'd take it in and the service guy would "clean" the foot pedal. Then it worked for about a year or so. The last time - he cleaned it and I brought it home. Started to sew and it did it again. Took machine back - got a new foot pedal (standard). Machine did it again. Went back - bought 2 yr old Janome 4800. They didn't want my machine for trade so I took it home believing it was a failed "resistor". Finally after 7 years - couldn't bear to part with my old faithful - I found a repairman who worked on the old Pfaffs.
I'd been told that it might be hundreds of dollar to fix th problem. $38 later IT'S PERFECT! He put the old foot pedal back on - the new one was too light power-wise - cleaned and tuned up all moving parts - and was told it was set for another 30 years. Seems the wiring was loose.
Colour me HAPPY:)
I'm suppposed to send it out west to my daughter for her to use till she can afford a new machine - but I'm not sure I can bear to part with it. Think it would be perfect for quilting with the dual feed and heavy duty .... sigh