One thing that can cause a rough idle

RockinRobin said

Hmm, I've had it hooked up several times, but I don't recall seeing that diagnostic function. Thanks, I'll look for it.

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Mine started missing one day and the computer was showing that it was only charging at 12.3 volts. It was also showing which coils were misfiring.
A new voltage regulator got it back to 14+ volts and all is well.