The modulator is on the side of the transmission (drivers side forward).

I recently wrote a lengthy description of the multiple adjustments on a 300SD. The situation is similar for the 190D. I wouldn't suggest playing with anything other than the modulator (it has distinct positions so it can easily be reset to original. The other adjustments can't be as easily retraced.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician