"HERE, "ran like a sewing machine" has always been understood to mean it ran excellent, well tuned, smooth and in balance"

That's what I thought he meant as well.  And that's how my '91 Rangers ran - "like a sewing machine" - smooth, well-tuned, no engine problems.  I don't think you could kill the engine in the Rangers I had.  (V6 , 3.0L)