Paul, to the right of the yellow circle is the throttle linkage (armature).

I copied this photo from the forum, although it is not a 79 300D, the linkage looks similar so you can locate it on your 79 300D.

Attached Thumbnails

 

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD