oven not staying on after ignition?

nw601g mod no444441475 to light oven press in and turn knob.
gas flows.igniter clicks and lights gas. but on releasing the knob,gas flow stops and igniter clicks away until knob is returned to off. if on pressing and turning knob. a piece of wood was to stop the knob from returning the oven can be used. i require a part number for defective item.