scan shows a p302 code, engine shutters and backfires. changed spark plugs and still does it

Question

pulled new plugs out and they are covered in a black soot. Intake manifold gasket was replaced 4 months ago.

Answer 1

When the sparkplugs are covered in black soot that is a indication of a engine that is  running , the engine would run rich for 2 reason there is a lean condition where a vacuum leak is causing the fuel management to add fuel, or fuel is being leaked into the engine system from places such as the fuel pressure regulator that is leaking and allowing fuel into the intake system,