If there's not a Bowden cable, I believe there is a series of rods running from the accelerator linkage on the valve cover, down thru the intake manifold and back to the transmission. Those rods can be adjusted in length.
Have you checked to make sure the kickdown switch is not stuck on?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13