98 Expedition, 130,000 miles, NEW plugs installed at 100,000. Rough idling began and I had it scanned. Bank 1 Sensor 1, then Bank 2 sensor 2, at this point I had all 4 O2 sensors replaced. After I replaced the sensors I noticed a Intake Manifold bolt that was broken off and could hear it leaking. I removed the Intake found that the Manifold had warped, so I had it re-surfaced. Reinstalled Intake with all NEW gaskets and it still had a Rough Idle.I then replaced the Idle Control Valve.It still had a Rough Idle. I remember a hose that was at the rear of the Intake that I had to remove and reinstall during the replacement of the Manifold.With the engine running I sprayed some carb cleaner near the rear of the Intake Manifold and the Idle improved, so I replaced this hose which goes from the back of the Intake to the passenger side valve cover. That was the problem.My Expedition is back to normal. Rough Idle fixed with Ford Genuine Part # F75Z-6C324-JA.

 

Great post. I have a rough idle too and will now be checking everything you listed. Its nice to see someone post not only a problem but what fixed it as well.

Thanks!!