Ok,
I have a 1997 S420 - I've noticed an issue with the idle at startup - particularly when it is hot outside (over 90). The car starts really rough (feels like dropping a cylinder) then as it "warms up" - it smoothes out, it's always had a bit of a miss in the idle (like, REALLY minor - I'm the only one that can notice it) and when it starts rough it smells really gassy (which could just be attributed to too much unburnt fuel passing out the tailpipe - since it clearly is missing)

I've checked as well as I can the vacuum lines
and replaced the temp sending unit (changed it unrelated to this issue - but I've noticed this problem before changing the temp sending unit.)
I have a new purge valve on order (since I would wager the one in the car is original)

Anything else I should look into?

Adam