I rechecked ep. 1.22 and it's definitely not in that episode. I was right, the ambulance goes by on a deserted street. Based on your description, though, I should be able to find it as I go through seasons 2 & 3, and I'm going through season 2 now. But there are plenty of ambulances all through this show (the Bluths are a pretty clumsy family) so I'm sure I'll find it.