P1131 & P1000 Code...

P1131 is an indication that bank 1 is running lean. Bank 1 is the passenger side. Double check for vacuum leaks. Make sure you don't have any exhaust leakage near the bank 1 sensor 1 area. Also, don't neglect to have a fuel injector pressure drop test performed. You may have one or more injector inlet screens fouled up. Injector lean out can sneak up on you and ultimately hurt your engine. It happened to a buddy of mine on his '00 GT. As for directly testing the sensor and it's circuit, it helps to have a scanner where you can watch the sensor in question while you do a quick snap rev of the engine you should observe the sensor voltage rise nearly immediately, alternatively you can use a short shot of carb cleaner into a vacuum line and the sensor should respond instantly as well. If it will do that, then something is up with the engine or injector/s. If the sensor does not respond then it is either a faulty sensor or a wiring harness fault.