This one: http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1FX0MB1RS1IZ0MGPA4&year=1991&make=MB&model=190-E-005&category=G&part=Engine+Temp.+Sensor
controls the Aux. fan.
And one of these: http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1FX0MB1RS1IZ0MNC8Z&year=1991&make=MB&model=190-E-005&category=C&part=Water+Temp.+Sensor&appEngines=_any
controls fuel injection based on engine temp.

From the Fast Lane catalog (top of the page).

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/showpost.php?p=831799&postcount=13
http://www.peachparts.com/shopforum/showpost.php?p=831807&postcount=14