I've got a 99 5.4 and it has a rough idle. I never really paid much attention until I rode in my buddies f150 with the same engine and it idled smooth as silk. The rpms don't fluctuate at all. They hold steady right at 700rpms at idle. My whole truck vibrates when it idles. Change in my cupholder will rattle and what not. Does anybody have any experience with this issue or know what it might be?

 

Tune up plugs fuel filter
Vacuum leaks Hose leak. Intake gaskets
Dirty injectors

 

MAF
IAC
TPS
Bad motor mounts
Oxygen sensors
Clogged cats
Misfire
Low Compression
Weak Coil

I have the same problem and haven't figured it out yet.

 

Same here replaced iac new mounts new coils and plugs
New engine!
I think its exhaust related. Maybe clogged cat or bad o2

 

My 03 5.4L's vacuum tubes from the 4x2/4x4 solenoids to front diff were broken. I replaced the tubes today and it fixed the 4WD swtiching issue, also it fixed the rough idle issue.
Last week I replaced the IAC, cleaned the MAF, throttle body, but those work didn't fix rough idle.

 

I think you're right about it being exhausted related because I had a new shorter muffler installed and I noticed the same thing. It was rattling on my cross member and I fixed it cutting a bigger slot for the exhaust pipe to hangout in and I haven't had no trouble with it since

 

I had a similar problem a few years ago, but mine would idle rough and the only way to keep it going was to keep pumping the gas. Turned out my Idler Air Control Valve. Not a tough DIY project, on the 5.4, it's on the back of the engine on the passenger side, just a really tough spot to work in. After I changed that, everything worked like a charm.

 

Yea. That happens. But he's not reporting the symptoms of a failing IAC. RPM's will fluctuate like you experienced and even stall out. Not the case with a steady RPM's and vibrations.

I did order a "F75z9d289aa Tube Assembly - Fuel Vap Oem Ford" as mine is in rough shape. This is the hose the connect from the throttle body to the evap canister as mines in rough shape. Wonder if there is a little leak. IDK.

 

No MIL ? or CEL ? How does it drive in comparison to your buddies ? Is the problem just at idle ?

Something like that. I'd take the EGR loose enough to slip a plate in between the throttle body elbow and EGR valve. That quickly eliminates this from being EGR related completely. Since there's really no other way unless you can read parameters.

The from there, go right to the ignition and verify any type of magnetic disturbance or radio frequency interference. They reak havoc on the ignition sytem and since your idle is on the low side (729/730 is perfect), I suspect what's been mentioned above, or perhaps something being plugged. But more so, yea,- a disturbance or interference more than likley.

Check the RFI disruptor connection. A simple continuity test. Disconnect the passenger side, then driverside. Set your multi meter to beep mode and check continuity from left to right side. They SHOULD be interconnected. The RFI's wrap the entire main ignition harness. You shuld get a good solid beep. I'm just using the beep mode vs true resistance as it only needs the connection.

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Next check over by your AC accumulator. Part of the ignition harness loops just above it sometimes coming in contact with. If you can't see any damage to the harness, pull or zip tie the harness as far away from the accumulator as possible. Do this with the vehicle running and listen for any changes in idle while doing so. This is also a common place for interference and or mag disturbance.

 

Once the rpms rise above idle, like taking off from a red light, you can't even tell there is a problem. And when it is at idle it doesn't seem to be really struggling if that makes sense. It just has shakiness to it.