I've changed almost every hose and vacuum line on my '89 560 SEL in the past 7 months. Lost count of the number, but each new hose improved the idle or performance. The biggest help was the short hoses to and from the idle control valve. O-ring on the oil dipstick cleaned up the engine. When I started, the old hoses were so brittle that I thought most of them were made from molded bakelite. Phil at FastLane was a great help in gathering all the vacuum parts. Good luck.
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)