Bought my '04 Lariat w/5.4 auto 3 months ago. It has 34,000 miles. Had it at the dealership today about the rough idle in drive and park. Tach shows under 500 rpm at idle ( which is too low) and a very noticable engine quiver. They scoped the engine and say they have found nothing wrong and the service writer says he's seen several other new 5.4's experiancing the same condition...but has no answer as to how to solve it. I had a 1998 Expidetion 5.4 with 208,000 miles you could eat dinner off the engine . What are they missing ??? Is this a common problem with the new 5.4? Got any suggestions?

Preston

 

I also have this problem but have not had the time to trouble shoot. I have an 05 with the 5.4 Supercrew. I would like to know how to fix. I thought about changing the plugs but I only have 47000 miles and did not know if it was time.

 

Rough idle condition is common with the 3V 5.4L engines. My '06 Expy has the problem and has since day one. Some dealers have had luck fixing the issue by replacing the engine mounts and/or adjusting the idle speed.

 

I have seen this also. It appears that sometimes the IAC valve gets messed up. What they did for my 04' FX4 5.4L was they replaced the entire throttle body with a new IAC valve included. This fixed my problem 100% and I have not had an issue since. Mine was stalling occassionally and the idle stumbled when coming to a stop. Hope this helps.

Mr86GT

 

I had the same problem about a week ago. Rough and low idle, no codes. It is a real simple fix. All I had to do was take off my air intake to get to my throttle body and then take it completely off and clean it really good with some carburetor cleaner. Then clean the hole into your intake manifold and that is all you have to do. But the big thing while you are doing this is to disconect your battery so that your computer will reset itself and recognize that you have cleaned the throttle body. But that should fix the problem for you.