I ran those instructions in the link and it had no effect on my issue. BUT, last night my subaru finally threw an error code. YES! “P0170” = Fuel Trim Malfunction (Bank 1). Called the local dealer and they said the cause is almost always the front oxygen (O2) sensor, but there was a chance it could be something else and the only way to know for sure was to bring it in for a full diagnostic. So, you are probably right jlapro. 
I’m planning on replacing the front O2 sensor tonight and if that fails, then I’ll bring it in. The car has 150,000 miles on it, so the O2 sensors are probably both due for replacement anyway.
I’ll post back on the results.