I'm not sure, but I think I found an error in the Durametric software's Motronic fault code reporting. I was getting a pair of codes on a fairly regular basis. I
think they happened together. As reported by Durametric 5.1.40 for my 1998 986:
P1121 Porsche fault code 430 - Throttle position sensor 1
P0160 Porsche fault code 20 - O2 sensor behind cat. conv.
But while scouring the web for possible solutions, I found a page that listed code 1121 not as a throttle position sensor error, but rather this for the pair:
P1121 Oxygen Sensor Heating 2 After Catalytic Converter - Below Lower Limit
P0160 Oxygen Sensor After Catalytic Converter (Cylinders 4 - 6) - Interruption of Signal
Now that makes more sense--nothing to do with the throttle position sensor if that's correct. All about the post-cat O2 sensor. I've replaced the sensor and await a hundred or so miles of CEL-free driving so that I can pass a smog test!
Here's the page with the info. The author is Randall who I think might be a frequenter of 986forum.
Boxster Check Engine Light Codes