First, if it's a craigslist ad missing, please see the missing posts answer in the SearchTempest FAQ. (The craigslist results are powered by SearchTempest.) Keep in mind that SearchTempest needs to use keywords to find posts matching your search. So if you search for a 1990 Toyota Supra, SearchTempest will search for "1990", "Toyota", and "Supra". If those words don't appear in the post, it won't show up. (However, you do have the option to tweak the auto-generated keywords if they don't make sense.) Also, to avoid false matches, it will only look for the make and model name in the title of the post, not the body. You can change that once you click through to SearchTempest though.
Otherwise, the most likely explanation is that you've set an option such as maybe max mileage or body style, which is filtering out the result you're expecting to see.
If you still can't find the ad, please feel free to get a hold of us, and let us know which ad you expect to see but don't. We'll look into it ASAP. Please include the URL (link) to your AutoTempest results page, so we can see exactly what you're seeing.
Finally, please note that neither AutoTempest nor our partner SearchTempest is affiliated with or endorsed by craigslist.