Try unplugging your foot pedal from your machine. Clean the plug, check to see of the cord is in good condition. Clean the pedal for fuzz/threads.
When you take it to the shop, ask them for one of the pedals and plug it in your machine..,.or go t Sears and ask to try one of their pedals to see if it works OK.
Buying a new pedal is better than paying for a trip to the shop...and you can get those through Sears parts or on line...
Diana