It might be the same problem I am trying to solve. If the cooling fans in the back are not working (not the fan by the element), then the oven will heat up, but as the back of the oven is also geeting too hot the temperature control is keeping the oven cooler than you expect. The worrying thing is that the back of the oven can be getting hot and it is unrevealed. It would be safer if when there is no cooling the oven stops working.There is evidence of too much heat build up in ours.
I thing the reason for the fans not working is related to the inside bulb blowing which can damage other components. I need a wiring diagram or a detailed service manual if anyone has one.
Phil Moses, May 2010