The discussion at the site below has to do with 380SL but may offer a few starting points. Certainly the suggestion as to where to look on the service CD will apply. Hope this helps-

http://www.slack.net/~thundt/mercedes/high_idle_hell.htm

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)