Originally Posted by kaboom10
Sounds like a coil is on its way out. They short but don't fail and don't throw a code. Look for a vacuum leak next. Start with the PCV line. Oh clean the MAF with MAF cleaner to. If it's dirty it can do all sorts of strange things.
Thanks for the input. Wouldn't a failing coil cause the same miss in neutral/park rather than in gear with a foot on the brake and be much worse under load? I've checked for vac leaks and it was fine. I will look into that MAF cleaning though, the previous owner had just serviced the K & N filter before I bought it and maybe he got overzealous with the oil. I've read up a bit on the problem elsewhere and there's several owners that have had the same glitchy idle 'in gear only' since their vehicles were new. A Ford tech said the cam profile is a bit aggressive on the 4.6L for more low end torque and it can show up in the idle.