It very well could be a bad thermostat, with older machines that are completely mechanical that is a lot of time the only part that controls temperature. Check to make sure theRe is no shorted terminal on the element itself and also check that the thermostat bulb has not fallen from its bracket. Sometimes these scenarios can cause similar problems. Lastly if the thermostat is indeed bad with no calibration screw of any sort you may be able to find a generic to fit the oven, though this is a lot more difficult than it sounds. You must make sure it has the same terminals, mounts the same, and has the appropriate bulb length to fit the bracket, and same length of bulb tube so it can reach the desired mounting are. These are best found through a parts catalog with generic part manufacturers.