Why does your 1983 Oldsmobile Delta 88 with 5.0 liter engine knock while idling.The slightest advance in gas it stops knocking.?

Why does your 1983 Oldsmobile Delta 88 with 5.0 liter engine knock while idling.The slightest advance in gas it stops knocking.?
check timing, gas octane, next look at worn connecting rods