Looking for classic M-B oppos (I know you're out there!) *High Idle Hell*

Currently looking at this 1989 420SEL for $3,000 cdn, been talking to the owner, and it suffers from “high idle hell”, which is apparently a common theme among these types of cars. He says it will idle at 2k rpm for a few minutes:

“Starts after couple of pushings of gas pedal and requires to hold it at around 2000 rpm…