97 Mercedes E320, 162k miles. When starting cold and having to idle, while in drive, during the warm up, like at a stop light when the temp hits 80, you will feel the idle slightly drop and the check engine light comes on with a code P0410 - Secondary Air Injection System Malfunction, lights up. If the code is cleared while the car is warm it will not come on again until the next cold start. It has no other runability indications, hot or cold. I have been told told by shops anything from "It needs a new wiring harness" to "It has a Mysterios vacuum leak and that may take days and over 10 hours to diagnose" Any suggestions for less costly cures?

They're are 11 pages of discussions on this very subject.
http://www.peachparts.com/shopforum/search.php?searchid=1736377
Read some and you will have a pretty good understanding of what triggers that code.
Probably save you a lot of money too.

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2007 C 230 Sport.