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What is the engine compression on that cylinder?
What is engine vacuum at idle?
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We had one that had a bad crank position sensor. It was giving a bad signal to ecm and kept getting a misfire on #5. Not sure if that is your case but we need to keep it in mind.
Did you try a new plug by chance, does not happen too often but will lead you in wrong direction. Does not sound like a weak cylinder it would be a dead miss at idle. This acts like the old cars when the points would bounce... New cars have crank and cam sensors.
Here is some ammo for you
Inductive sensor with a permanent magnet Resistance 125.5 ±17 Ohms
2 wire sensor. Produces an ac voltage signal.