My car is still getting a 2413 error code every now and then... HELP!!!! UPDATE, but still no fix!

[Levent Cur]

Hello All, 
 
            My 1995 S6 is still having a problem with the error code
2413, meaning that it is running rich! I changed the O2 sensor with a
brand new audi one about 200 miles ago, the exhaust smells real bad like
rotten eggs cause of the rich fuel mixture, and I have an MTM Stage 1
upgrade!  I also have a silicon lower intercooler hose. And it is
clamped down 100% of perfect, there is no loss of power! But I keep
getting that darn 2413 error code every now and then, and it upsets me,
the car seems to be running fine.  I only put Amoco 93 octane gas in
from the same station, and even tried switching to Shell with their 93
octane. Still the same!!! HELP!!!! Any an d all of you guys plz help!!!!

 
--Levent-
 
UPDATE:
 
I let the car sit outside for 30 minutes in idle. And the car prior to
turning it on and letting it sit outside there were no error codes
returned a 4444, but after i brought it in, the 2413 error code
appeared! Any ideas?
 
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