I would look further for other factors.
I've put adsense up and pulled it and put it up and.. etc.... Google would not penalize you for this, because they want you to be able to properly test your results, change things around, try ads in different places, and be free to design your site and redesign it. I've never noticed a huge ranking difference from that.
It could have been a coincidence that's unrelated?
What might happen that would cause it accidentally, adsense scans the site's text for it's content, and displays ads relevant to the content, thereby adding more relevant keywords... Is it possible, the keywords from the ads themselves were helping your rankings? If this is the case, you could replace them with text when pulling them and put something like "*keywords* ads go here" ?
I wouldn't put it past Google to scan for sites for sale with a bot, and reduce rankings if your site is known to be for sale.... but I have not heard of this happening.
Is there anything else you changed? Did you accidentally cause an error somewhere or something?