I have both of these cars and the same experience as the Thread writer; the 89 420 has a slight roughness in the idle, not a shaking or anything -- but runs very well otherwise. (perhaps I need to run a can of the super cleaner through it? My 300CE idles smoothly.... Ben Carter

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Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)