1989 300e high idle

Help please: I purchased from Mercedes the Service Manual cd for subject car. I have the inline 6 cyl body 124 engine # 103983.
This am I replaced the idle valve Bosch part #0280140510. It did
not help. With a/c off and trans in park it idles about 1300 to 1500. In gear with a/c on about 750 this condition is hot or cold and when hot if it sets for 15 to 30 minutes it is very hard to start. When it does start it runs rough for 10 to 20 seconds. I have to get this fixed or my wive will want me to sell the car. I love the car. So far I have not been able to locate any info on the cd service manual.
Thanks in advance
Darryl

[vrsmith]

Mine had a fast idle that was cured by replacing the throttle
cut off switch. It was about $15. Other suspects are the
O2 sensor, airflow sensor and throttle body switch. All
are expensive.
Good luck.

[Mike Murrell]

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