ECU is shutting down a cylinder (99s320)
 

What would cause this? Just trying to have a clue before I take it in....:confused:

when missfire is detected [those engines have plug wire issues] the ecu shuts down the offending cylinder injector.

Most likely, it's a bad plug-wire set for that cylinder. As David said, there's problems with the "wires". :mad:

Saw this first hand and had a hard time believing what I saw at my tech's shop. The plug wire looked ok but it was open! And they only 8" or so, amazing!

The problem is the resistor boot under the coils..very common on this last of the Waste Spark ignition DIS systems.
Change all 3 of them. [ one under each coil /DIS system]
Leave the plug wires alone until you change these 3 coil connectors.
Techs change these automatically when doing plugs change on 104's b/c of their failure rate.

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=2AO123CS42BD0O5777&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1999&product=F1010-84561&application=000357360

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Spark%20Plug%20Connector&url=http%3A//img.eautopartscatalog.com/live/F101084561BER.JPG

I would also change the plugs while I was there b/c these great systems still take the Bosch NON Resistor Super Core plugs and they are dirt cheap..use NO OTHER but F8DC4 in 104 DIS engines..they love this plug

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2AO123CS42BD0OD395&year=1999&make=MB&model=S-320-001&category=F&part=Spark+Plug