not sure about '99s but I know the older ones had issues with the EGR valve getting gummed up with carbon, ultimately leading to burnt exhaust valve(s).
By the way, for the Metro owners here, what do you usually do about this, just clean your EGR valve regularly or something? Can you just spray some carb cleaner in there to clean it out?
If it's not too late, do a search - someone asked "what to look for in a Metro" a while back and XFi and I put together a pretty comprehensive list of stuff.
I definately remember that, you should ask him permission to use that and write up a mini-buyers guide for your site (and hey, there's an idea for mine).