I've been driving about 1500 miles with the factory plugs on the custom tune I got from Unleashed tuning and I've been experiencing rough idle on all tune levels from 87 to 91...even on the canned tunes. Replaced factory plugs out with the Ford Motorcraft Iridium plugs today...so much smoother at idle now...Factory plugs weren't all that bad honestly for 70K miles. Gaps were a tiny bit off...roughly .035 - .037 when .030 was needed...insulators were not cracked...and looked pretty good.

 

I am amazed they look that good at 70k miles. I'm at 51k miles and am on plug set #3 but I've been tuned almost since new. You will love the Unleashed tunes even more now that you've got proper spark.

FYI, change them every 15-20k at most.

 

I'm surprised too! I changed mine at 35k and the truck was still stock and they didn't look that clean!

 

What Motorcraft part number is associated with the iridium plugs?

 

sp-534