My car keeps throwing this code, but seems to be running just fine.

I have no cat, but straight pipe to the muffler.

When it threw the code the last time, I checked the fuel trim:

Short term Fuel Trim B1: 1.55%
Long term Fuel Trim B1: -0.00%

Do I need to buy a "dummy" O2 sensor? If so, where can I find one?

Anyone have a suggestion?