1990 Ford Bronco Misfiring

Replacing random parts is not a good way to diagnose anything. First I'd consider grounding each spark plug wire, one at a time, to see if only one has no effect on how the engine idles. If each one makes the engine idle worse when it's disabled, suspect a fuel pressure problem or erratic ignition timing. If one cylinder doesn't cause a change when it is disabled, perform a compression test. Burned valves, a worn lobe on the camshaft, or a worn rocker arm will cause a misfire.

If your engine uses a knock sensor, a mechanical knock that you're hearing will lead to the Engine Computer retarding ignition timing, and that will reduce power.