Shaking '95 C280

My car has a problem with shaking when the brake is used. Usually the shaking only occurs whenever i turn my car and the AC is already on or whenever stuck in traffic. The shaking gets worse during the summer because of the hot weather and shakes more if i keep it outside. My mechanic does not understand why the car shakes. He thought it was because a sparkplug wasn’t in place, but the sparkplug was fixed and the car is not any better. If anyone has ANY suggestions i would appreciate them as this has been occuring for years.

Have someone check all the vacuum lines.

the vacuum line was just fixed and the car started working well again but recently it started shaking again.