I drive a c220 cdi w204. Mileage is 60,000 km. Recently, the vehicle has started going in to "limp mode" when starting up in the morning. The temp gauge does not move at all. After driving for a few kilometers, the temp gauge moves and the car returns to normal. It's summer here now, so no cold temps. Somebody advised changing the car keys. I used the spare. It has not helped. On board computer and Diagnostics do not show any errors. What could be the problem?