I have a 1997 E300D that runs great the majority of the time. The only problem is that when you go the same speed for a while say 55mph the car starts to surge slightly, until you either speed up or slow down then it stops. You can gas the car and it runs great until you plane out at a certain speed then it begins to start surging again. I have changed the spin on fuel filter and the pre-filter with o-ring. I have changed the egr, I have taken the intake off to look for broken vaccum lines but I have found nothing. I didn't put my tester on it and it had a code that read Fuel Temp Sensor Malfunction. Does anybody know what that is or have any suggesttions? Could that be the problem?