91 Firebird suddenly hesitates badly

My 91 Firebird 2 brl injection 5.0L 134K has suddenly started hesitating badly. Will barely stay idling but will rev up okay in neutral. Once rolling, nearly stalls when accellerator pressed. Seems to get better when engine heats up. Will occasionally start running near normally after warm. Replaced fuel filter but no change. New plugs last year. Checked failure codes and O2 sensor came up. Cleared codes then drove more. No failure codes come up. When running in field service mode, indicates open loop at first, then alternates between lean and rich indication. Any advice?

Reply to
smokinleroy
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Vacuum leak, bad injector, bad coolant temp sensor, bad plug wires, bad connection somewhere, bad/plugged catcon, etc. GW

Reply to
Geoff Welsh

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