Hi,
The fault code does refer to the upstream sensor. It will remain on until it is cleared, so is probably from your earlier problem.
If there are no misfire fault codes or other sensor failure codes it suggests that the idle is out of wack.
Theoretically a low idle should prompt the idle control valve (Iacv)(aka the stepper motor) to try to lift the idle speed to prevent stalling.
So two possible problems 1. The iacv is not working. 2. The base idle speed is way too low.
The idle could be low from a restricted air flow, is the air filter good and clean?
You can adjust the base idle with the set screw on the throttle body. Disconnect the iacv plug when the engine is up to temp.Check idle. Turn the screw a quarter turn at a time and recheck idle speed. Base idle should be 850-875rpm.
Plug the iacv back in and observe the idle speed. It should settle at 875-890 rpm.. If the iacv is working it may take a while to settle and change step several time over a few minutes.
If the final idle is way out., you may have to repeat the process until you have a stable idle in the 875-890 range.
If plugging the iacv in and out has no effect the iacv may be duff. Sometimes cleaning it with carb. cleaner will free the valve. If not replace it.