I have a friend who has a w115 240d that accelerates faster then my w123 240d he said it was because of a kickdown or kickback switch (i forgot the name) so i was curious is that the reason, if so is it bad for the engine? and if its not the switch then what could be the other reason?

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold