Is there an adjustment or vacuum line on my Mercedes 190E that will make it shift hard and how do you find it?

Yes, the Mercedes 190E may have a vacuum line that affects shifting behavior, particularly if it has an automatic transmission. A hard shift can be caused by a vacuum leak or a malfunctioning vacuum modulator. To find the line, inspect the engine bay for rubber hoses connected to the transmission and intake manifold; look for any cracks or disconnections. Additionally, consult the vehicle's service manual for specific diagrams and locations tailored to your model.