A 1985 300TD does not have any accelerator cable. Its a metal linkage with joints and rods....it must be carefully adjusted to move properly....this can take a long while to get right, even for someone who is familiar with it. The "cable" you see is the bowden cable, it is correctly functioning, it pulls out as the throttle is applied to tell the transmission how long to hold each shift point...if the car is shifting correctly, do not mess with it.

On a W123, a soft pedal/bad response can often be due to the rubber throttle bushing on the firewall having come apart and flexing when the throttle is applied. This is the part:

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