aaah, the good old 'Italian tuneup'

Works for some, not for others, but if you dont drive only highway miles at reasonably hgh speeds, my bet is theres carbon and junk effecting your engine's operation, and soem good hard running will indeed help.
Even if you do drive a lot of highway, I had the 300D up to 85-90 for about an hour while down in TN, and it definitely drove with more power and pep than before.

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)