CIS 1, Sixto 0. I had a '91 300SE with a turbine smooth M103. Then the idle was less than smooth and economy gauge was close to middle when idling. Full valve job and replacing everything short of the fuel distributor didn't fix it. I wasn't about to buy a new fuel distributor so I sold it and never looked back. While I'm bashing, it got 16/21 mpg. The '95 S420 that replaced it got 15/22. Good engine in its day but not a good fit and maddening gear ratios in a 126.

Sixto
83 300SD can be yours
98 E320 wagon