Uncomfortable ride

[Toby]

We own two 190 E’s both built in 1983, one in June and one in October. The first car is a standard 2 litre automatic with 110.000 km . Whereas the second car was tuned by AMG for 160 BHP by enlarging it to 2.3 litres; it is a manual with 230.000 km. What we would like to know is: why does the standard 190E drive much more smoothly and effortlessly than the AMG tuned one, which seems to work much harder and does not glide as easily and refinedly as the regular one. There is a considerable difference of behaviour between the two. Especially since the suspension has not been touched. Both cars have been in our family since day one.
It is a puzzle to us why the standard car floats like on air and the tuned car behaves so much more cumbersome and heavily, it has been like this since we got them.
We thank you for any help.