have a misfire wen idling what is the cause of it?

Hi guys please I have a 320i chrome bumper 86 automatic have a misfire wen idling what is the cause of it?

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[Nick at Pelican Parts]

Try to unplug each injector one at a time (look up the Pelican procedure for removing injector but just unplug it electrically) and make sure the rpm drops equally every time an injector is unplugged. The cylinder that doesn't drop the rpm is the problem cylinder , then check spark, fuel injector pulse and compression

- Nick