Got the CEL with a P0172 code a week ago. "Fuel trim
malfunction (A/F too rich)". Cleared and so far it hasn't
come back. At this point, what is better:

1. Not bother with anything until it comes back again?
2. Start checking and investigating?

There doesn't seem to be anything wrong with the car.
Maybe, just maybe, a little rough idling thouhg.
Is it, by any chance, a common code that tends to be
triggered by one particular component on Subarus?

DK