want to search across all of craig's list for a specific model using google? It takes two steps...
First, type this into your search box:
site:craigslist.org mercedes "220d"
Second, change the date range. Under the entry box at top click on "search tools". the line below that will say something like "any time". Change that pull down to read "past month".

Bookmark the resulting search page. You might want to run though those ads first and then change the date range to be the past week.

-cth

.