All,
I replaced all 8 plugs and coils just before a 100k. All 8 broke. Used the Lisle to get them out. Afterwards I had compression leak and fuel smell in cab. Pulled coils and torqued plugs to 25. Used Universal joints on the sockets. Three weeks later I felt like I would still get a gas smell once and a while. Pulled all coils found one that smelled of gas and had residue on it. Retorqued all to 25 without using joints. That way I knew I was really getting 25ft/lbs.

Anyway when I finished the first time I found a mushroom shaped cap on the ground, which I have since misplaced. I have looked through the forum and found a picture of one used to plug a vacuum line on a 2 wheel drive truck. Mine is a 04 FX4 Screw 5.4 3v.

The past three days it has just started getting down in the 40-50's in the am. Truck starts up and runs fine for 5 minutes to a 1/2 mile. Then the idle turns horrible for 30 seconds, couple missfires. Then it clears up and runs great the rest of the day. It is like once it starts to warm up it goes awary for 1/2 a minute.

Two questions. What vacuum line needs this plug, and could this cause my symptoms?

Thanks

See pic I found on the forum of what the plug looks like.

 

Went to dealer and they had a mechanic come out and look as well. He doesn't know where it belongs either. He agreed there would be one up by the intake on two wheel drive trucks. Being as mine is four wheel, that line is hooked up. I don't buy the fact that someone accidently dropped it under the hood and it has been rattling around in there for 7 years and 105,000 miles without falling out.

It had the same issue with the misfire this morning.

 

that plug looks a lot like the piece that holds the wire harness to the valve cover, check those you should have 2 on each side. they press down on to a stud

 

Those are Rounded and smooth on the top of the head and have little wholes in them.

 

Ok, and just an fyi on my 05 2wd 5.4 I do not have any sort of red vacuum line like in the pic

 

Yep the 04's had a different vacuum line pickup point than the other years.