Originally Posted by jcyuhn

The pin 8 code 13 fault indicates the engine computer has reached the maximum limit to which it will enrich or lean out the mixture. Your car is obviously running on the rich side. The code does not directly implicate the O2 sensor; the computer is not seeing an open circuit or otherwise implausible signal from the O2 sensor.

There's quite a few threads on this fault, here's one: http://www.peachparts.com/shopforum/tech-help/128161-m104-pin-8-code-13-question.html

I suggest using google to dredge through past threads here, search on "m104 pin 8 code 13 site:peachparts.com" for reading fun.

Good luck.