Originally Posted by Ted_Grozier

The miniature "shock absorber" on the injection pump is designed to slow the linkage down if you release the accelerator quickly. It is only fitted to manual transmission models and improves smoothness during shifting and creeping in first gear.

Some of the folks who have converted automatic 300Ds to manual trans report that the revs fall of too quickly, making smooth shifts difficult. They blame this on the turbo not "staying on boost." I think instead that the problem (minor or not) has to do with using the lighter 240D flywheel and not retrofitting this mini shock absorber to the IP linkage. The 300D manual cars from the factory (non-turbo, Europe-only) came with this dashpot.

For a thread devoted entirely to this discussion, see the dashpot: real reason turbo / manual cars weren't soldTed