Wind noise from the dashboard while presing gas pedal

1988 300CE (124)

For a some time already my car drives like s..t. Main problem is that when driving sometimes the car chokes even on the highway at speeds around 80 m.p.h. While driving at steady speed suddenly car slows down and to keep driving I have to release the gas pedal and than de-pres it again. Looks like to drive it I have to keep pumping the gas pedal every few seconds. This happens aften but not all the time. Yesterday I've noticed that there is some wind sound coming from the behind of deshboard at windshild. At first I though this is a fan or radio speaker noise. Turned everything OFF but the noise is still there. The only time it stops is when accelerating or presing the gas pedal down. Could that be vacum leak? Please someone help.