They did "diagnose" it but not fix it. They replaced the coil pack. That took care of the flashing check engine light and the rotten egg smell but not the misfire. Somehow they also managed to screw up the radio in the process, as the tweeters in the a-pillars cut in and out now. With the air (which barely works, and we've never been able to get that fixed either) on I had to floor it to make it over an overpass today. This is the wife's car and she needs it 5 days a week (schoolteacher) so getting it looked at means I have to get up an hour early to take her to work for however long it is in the shop. I am NOT happy.
The last day of school is Wednesday, we will be taking it to a different dealership to see if we can get this fixed.