OK, this is a subject I have been dealing for a year and a half now! My Dad is a Ford machanice of 32 years and I eventualy came down to this resault. My 2000 5.4 F-150 has the same problem, the dealership replaced a Harmonic balancer, a motor mount & a Torch converter. I got tired of the dealership and exstended warrenty issues so I gave it to my dad for one day. It basiclly was the Intake plenium gasket, when you spray carb cleaner at the front of the intake the idle smooths out that tells me that there is a leak. The gaskets have been replaced and it runs great now!

 

John,
Very interesting information.
Thank you.

 

First of all thanks everyone for your input. The dealer finaly figured it out. After 6 trips and several phone calls, they pulled out the plugs and found carbon tracking and rust on them. They replaced all 8 and one funny looking coil. It runs great. Maybe my gas mileage will go up. THANKS!

 

Its really hard to track the rough idle, because so many things can cause it.

Another thing I havent seen mentioned is the IAC, which can get plugged up and cause your idle RPMs to be too low. I cleaned mine out earlier this year and I used to idle at around 600 RPMs, now its closer to 700. It still gets low sometimes and I can feel the idle.

Sometime this summer Im going to tackle the spark plugs as well since I have 112k miles and I imagine they have not been changed yet.