P0171 System Too Lean Bank 1 Fixed
I checked for vacuum leaks and it turns out the small cap was missing from the vacuum fitting on the back of the intake manifold allowing a vacuum leak. Not sure when it was eliminated but the vacuum fitting hole on the side of the Air Cleaner Intake Resonator is sealed over. I idled the engine to confirm the vacuum leak and then slipped a rubber cap on the manifold fitting to block the leak. I used my scanner to delete the P0171 code and now the check engine light is off and the car has more power.
In the years before computers an engine with a vacuum leak that big would have run rough and most likely would have stalled at idle.