I have a 1997 E300D that runs great most of the time, my problem is that when your driving on the highway or anywhere you are at a certain speed (55-60mph) for a while the car begins to surge.(Not extremely bad, but bad enough you can feel it) When you accelerate the car or let of the gas the surging goes away. If you start at a redlight and hammer the car it runs perfect no matter how fast you go until you plane out and start running a constant speed then it begins to surge. I have changed the fuel filter and the pre-filter w/ oring. I have also changed the egr and taken the intake off to look for broken vaccumm lines and such. This hasn't fixed anything. I have added fuel system cleaner also. The car did have a code in it that said something to the nature of Fuel Temp. Sensor Malfunction. I erased it and it hasnt' returned but could that be the issue? Any suggestions would be great. Thanks