What can cause a slow acceleration in a Mercedes?

depending on model,

1. supercharger belt loose ( if supercharged)

2. drive belts loose

3. engine air\fuel sensors aren't calibrated correctly or need replaced.

4. engine oil hasn't been changed in a long time ( most likely)

5. engine is worn out

6. transmission worn out

7. fuel pump is clogged or needs replaced

8. cam timing is off

9. rear end needs lubricated

that should get you started