" I guess I could have replaced the spark plug wires too, but I replaced them about 30,000 miles ago and … "
For a Miata 30,000 miles is like 60 - 80,000 in most other cars. The Miata fires twice as often as most cars. It is an odd thing and it "waste" half of the sparks, but that is the design and that engine really runs nice with everything is as it should be.