Error Codes P1128 P0131 Oxygen Sensor Lean

[rcederblom]

This is a '99 2.0L 5sp with 87,000 mi. Full 40k tune up at 81k replaced spark plugs, plug wires & brake booster to manifold vac hose.
Check Engine:
P1128 LT Fuel Trim Too Lean
P0131 O2 Circuit Lo Volt Bank 1, Sensor 1

Is it likely it needs a before Cat Converter O2 Sensor?
Do I understand the after Cat O2 Sensor usually doesn't cause problems?

Any ideas or experience with this is appreciated.
Rod