How can I fix a heating problem with our YKEMC307KS0 oven?

We have a temperature control problem with our Kitchen Aid YKEMC307KS0 oven/microwave combo unit.
When you set the desired oven temperature and start the oven it heats to the desired temperature (beeping to indicate this), however it will not maintain this temperature. The oven temperature is allowed to drop below the desired temperature setting. It is necessary to continually reset the desired temperature and press the start button in order for the oven to heat back up to the desired temperature. When it reaches the desired temperature again the oven beeps again. Then a few minutes later you repeat the cycle… and so on… and so on.
Has anyone run across this problem and more importantly has someone found a solution?

JK
August 2013