I just put in two new upstream Denso O2 sensors this weekend. I was trying to resolve a few issues, all of which had O2 sensor as a possible culprit. Car has 113K miles so I figured it would be a good action to take.

Sensor I pulled form the passenger side was very black and sooty when I took it out.

Well, since replacing the O2 sensors, I am still getting a P0174 and P1133 code.

Any ideas what to look for?

Already done the following: plugs, wires, pcv system, new intake gaskets, paper air filter

Car has: SLP LID, BBK 80mmTB, BBK SSI Intake, factory tune