MB 1989 190E 2.6 hesitation
 

My MB 1989 190E 2.6 runs great until after driving 20 miles or so and then at speeds between 25 and 40 mph it starts to hesitate and surge like it is starving for gas. At these speeds it will hesitate on accleration. On the Interstate it runs fine. All though the cruise control will kick out on it's own some times. Idles fine. Could this be a vaccum problem or a clogged fuel filter? What about the fuel pump relay?

I finally figured out the problem. I had a bad altenator. Replace the devil and the problem went away.