Mercedes Benz repair: 1990 560 SEL runs rough up to 80 on temp gauge, number search results, catalytic converters

Question
I have a 90 560SEL gas. It starts fine and seems to run/drive ok at first but after a short period of time while engine temp is increasing it runs rough (seems like it may be misfiring) until temp gauge is just below 80 deg. then it cleans up and runs good. after reaching 80 deg. when coming to a stop and trying to accelerate it seems like it is either not getting enough air or is flooding out. accelerating from a full stop is very slow but this does not occur every time when at a full stop. I have changed plugs, cap rotor etc.  

Answer
The first thing to check with your symptoms is the Catalytic Converter.
This is suspiciously close to classic symptoms of a failing Catalytic Converter.


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1990 Mercedes Benz 560SEL
Part: Catalytic Converter
 Note:  Federal Only
Also need #BOSALWAR/CAT. "After-market" OBD II Catalytic Converters Not Legal for Sale in California 1995 ON     

H3000-74199 Catalytic Converter Federal Only A & B Auto Parts IN STOCK $605.13  
  
H3000-49563 Catalytic Converter Federal Only Bosal IN STOCK $532.33  

http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=cata...