Here's the background:

1998 Expedition 4x4
5.4 liter
57k miles

Mild miss at idle. Worse with air on. NO check engine light.
After reading through some posts, I've done visual checks throughout the engine bay looking for loose hoses, wires, ect to no avail. Any ideas on a place to start? I'm really not relishing the idea of pull all the plugs (although it is my first inclination) on a goose chase. I'll take whatever advice you guys feel would be prudent.

To make matters worse, this is my wife's truck So I HAVE to fix it NOW!!!

 

Here's a real old solution from Pkrwd that worked on my '99 with a rough idle.

If a wiring harness is touching the a/c accumulator tank, move it away from the tank. It cured my problem.

 

As a correction to my first post. The engine does more than miss at idle. It has been missing at all engine speeds. I could barely notice it the first time I took it for a test drive. After a later and longer test drive it really stood out.


A bit of an update:

I tracked down whoch cylinder has the miss. It's the second cyl. back on the paasenger side. (#6?) I pulled the COP and plug. Plug was dry and a little white. It had some carbon buildup on the electrode. I cleaned it up and put it back in. It runs a lot better. But, it still has a mild hiccup of a miss intermittently. I plan to do a complete service including plugs next week. (payday) I'm still wondering whether I have a bad COP that allowed the plug to build-up. Or, whether the plugs just need replaced. I bought the truck back in November last year and was told that it just had had a complete service. (I took it to mean plugs too.) Any ideas out there??

BTW, I'm going to have a look at the wiring harness in relationship to the a/c accumalator in the morning.

 

Not sure how much this helps, but my mom's suburban was having simlar problems. Her's was more during acceleration than anything else, but at times it was skip at idle. Just gave it a good tune up. Plugs, wire harness, rotor, and ended up replacing the wire from the alternator to the distributor. Atleast that's what the mechanic said. She took it into the shop before I could tell her I would do it for her. Fixed all her problems though. I think there was corrosion on the wires. Who knows??? Hope it helps.

 

With 54k miles you would be best served by doing a tune up. Servcie normally means oil and filters most of the time. Platinum plugs are suppost to go 60k + but they can start to have there problems when they get to the end of the useful life. If you can afford the plug wires you might as well do them too. ( why get dirty twice.) let us know!!

 

When you say wires, do you mean the boots and "springs" on the COPs?