Might as well toss another theory on the pile. A worn cam lobe (I've had this happen 3 times to me now, *SIGH*) that barely still opens the valve will allow the engine to run perfectly fine at lower throttle openings and at idle, where the cylinder can still get enough flow for the power setting (sometimes even more - less lift results in higher velocities, which can improve breathing at low RPM). But open it up and only then will the flow in that cylinder not match the others, resulting in what feels like a miss. This can be a bit tricky to diagnose at first, because typically you tinker with it at idle and its perfectly fine. Just pop off the valve cover, pull the coil wire, and crank the engine around a few times while you watch the valves open. By the time a worn cam lobe makes a difference in the way the engine runs, it is *very* evident to the eye.
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I'm JohnMc, and I approved this message.