Replaced Mazda 3 spark plugs a few days ago with NGK laser iridium per OEM spec at 105,000 miles - it was running great and old plugs looked great. After replacing plugs I've noticed a little less pickup and slightly lower mileage. I did not adjust gap as I understood they come gapped correctly and gap did look comparable to old plugs, Idles and runs fine but I feel like I am missing some power. Thoughts

 

Some plugs just dont perform as well as stock plugs, my former Saab ran like crap on the iridium split fires that I bought for it, took them out and put OEM plugs back in, no more issues and ran better. OEM parts are almost always a much better choice than the spendy aftermarket parts if everything else on your car is stock.