Well, you are right about the fault code.
The intriguing part is the ignition on engine off reading.
If you have a Cali. car it should be 85% (according to the manual). Otherwise 70%.
Engine running but cold should be 50%, and then oscillate after warm. (unless a fault, of course)
The sensor might be good, and there could be a wire problem. (I always check the wires first).
My 2 cents.
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car