it may be getting too much air. The auxillary air valve is supposed to shut once the coolant reaches a certain temperature. When warm, it does not allow any additional air in. Maybe is is not closing all the way. When warm and idling rough, try pinching the hose off and see it that makes a difference.

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Mark Herzig
1995 E300D 153K
1985 300D 142K (sold)
1979 450SL 122 miles (sold)
1992 500E 127K (sold)
1987 300SDL 132K (sold)
1986 300E 161K (sold)