If my memory serves me correctly, the electrode gap for Iridium spark plugs is smaller than for conventional spark plugs...to achieve the same working value. I had Iridium plugs for a while and I am now happily using standard plugs again. Don't get the electrode gap values mixed up.
You can tell very easily if you google a standard type for a Ford plug and look up the Iridium equivalent plug, the electrode gap is different. Just as an ifo, if I go by the values that Ford recommended for my 1.6 Sigma later, they always refer to conventional plugs if I see it correctly.
