Check out this thread - especially the comment from Steve Brotherton - 1st sentence in his comment. It says it all.
The vehicle in question in this post is not the same as yours - the concept is.

http://www.peachparts.com/shopforum/showthread.php?threadid=10452&highlight=fast+idle

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"