Let's back up.....HOW did you determine that the switch is the culprit?

Before getting carried away, check the usual suspects - vacuum leaks and idle air control. The latter is a very common issue for high idle, when the control board fails or the solenoid sticks, it sticks open and causes an idle 1200-1500 RPM.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)