Cruising through Mercedes stuff on eBay, lookie what I stumbled across!! With a "Buy it Now" price of $234, no less!!
Here's the description and, I'll assume, a list of the cars this adjustment technique
should work on.
"BOSCH Mercedes-Benz E.H.A. Valve -Governor Kit FREE S/H
This is a BOSCH Mercedes-Benz E.H.A. Valve (2 prong governor kit). It is mounted on the fuel distributor. Fits 190E 2.3 16-valve (86-87), 190E 2.3 (87-93), 190E 2.6 (87-93), 260E (87-89), 300CE (88-89), 300CE 24-valve (90-92), 300E 2.6 (90-92), 300E (86-92), 300E 4-matic (90-93), 300SE (88-91), 300SE 3.2 (92-93), 300SEL (88-91), 300SL (90-93), 300TE Wagon (88-92), 300TE 4-matic wagon (90-93), 400E (92-93), 400SE (1992), 400SEL (1993), 420SEL (86-91), 500E (92-93), 500SEL(92-93), 500SL (90-93), 560SEC (86-91), 560SEL (86-91), 560SL (86-89). Part# 000-070-3962"
Since discovering this adjustment, my gas mileage has increased by maybe 1 1/2 mpg. It's really too soon to tell, only one full tank. But the easier starting & smoother running is so o o much nicer, I'd take a reduction as a trade.
Enjoy,