did you have to run a power wire to you AF gauge? if so it is possible that there is an issue with that wire. especially because that wire is sometimes shared with the Sterio/amp wire. my guess is the problem lies there.
as for the tune i dont think that is the issue. the codes are prob manufacture specific and you need a master list to get the info from them... another possibility is there there are stored codes in the car right now and that is causing the issue. Have the car scanned for codes and repost what those codes are. have the codes reset. if they wont reset the codes unplug the battery for 30-45 min and that should wipe them out.
