Frigidaire oven overheating

I have frigidaire gas oven, model#fgf355cgse. new in 2000.
for the last couple of weeks, once in a while the oven works properly, but usually, no matter what temp we set the thermostat at it heats to self cleaning temp. no error codes come up on the digital display. is this a thermostat/regulator or do i need to replace the control unit?