I drive a 1987 190E 2.3-16. I have been having this problem lately where when I drive at highway speeds, sometimes I push on the pedal and it feels like I am getting no gas. Sometimes the feeling only lasts for a few seconds and then the car picks up and starts accelerating. Other times the car doesn't want to move throughout the whole pedal movement, even when I downshift. Downshifting doesn't give any acceleration at all when this problem starts to occur. It just raises the RPMs, but accelerates no faster than when in fourth gear. What could be wrong?