Re: 99 Navigator missing at idle .... ideas?
Bah to the oem plugs. Use any good brand name platinum plug. No need to pay for any of the "splitfire" "u-groove" or other high performance plugs as you don't need them and they serve no benefit to unmodified engines. (on a side not, "shitfire" plugs don't do anything beneficial anyway)
You can use autolite, motorcraft, denso, ngk, etc....
If you are going to do it yourself though, be ready for a project. There are some people that can do it without removal of the fuel rail, but most have to pull the rail to access at least the #6 plug