I am having a problem with my 1987 190 E 2.3 I think it might be the fuel pump but not sure. As I am accelerating down the highway usually past 65mph the car begins to bog down. Even if I depress the gas pedal to overcome this the car will not accelerate. If I release the gas pedal and try againg sometimes it clears the problem but sometimes it continues to bog down. What could be happening?