I have been trying to figure out what is causing a check engine light on my 96 850, and am running out of ideas. I took the car to the parts store, and they read code P0172, rich mixture from forward O2 sensor. The car is running extremely rich, especially when cold. I have to put my windows down after start to clear the fumes from the cabin when I start driving. I have done the following so far:

replaced spark plugs and air cleaner.

replaced thermostat (car was running cool in the cold weather, but is reaching correct temperature now).

Cleaned the throttle body. When I cleaned it, I found that the small rubber hose on the flame trap was rotted and split.

The richness problem still persists. Could the cracked flame trap hose be the reason? What does this hose do, and where does it go?

If I have a problem with vacuum, how do I know when I have found all of the leaks...what is a "good" vacuum reading for an 850?

What else could be causing my rich mixture?

Thanks in advance for any help!

Andy