My wife has a 2005 Expy 5.4 it idles a little rough but still smooth. The truck runs fine and everything but it just seams to idle a little rough, to the point you can feel it inside the truck. There is not codes or check engine light has never came on. has about 70,000 miles.

I ran some Lucas F/I cleaner through it but no change. Could this IAC valve be the cause , if so where would it be located, I am more of an older truck kinda guy.

 

You might have a COP going bad, or a plug itself. Has the engine bay recently gotten soaked? (ie, washing the engine bay)

 

No I havnt cleaned it sence we got it, I know I should but!!!. What is this COP that could be going bad

 

COP stands for Coil on Plug. Each plug has its own coil mounted on top of it.

 

I had ruff idling and it turned out to be a bad head on one side of the engine. Might want to check the compression to make sure its not this.

 

I had a rough idle with my new-to-me 72k mile '05 2WD EB. It would only happen at stopped, dead idle, in gear, with the AC off, after the engine was warmed up and in closed loop operation. I started with new plugs since I knew they were not changed anyway, however, a plug change didn't help. Coils and boots were still in great shape and I checked to see if there were any other mechanical issues; I had none.

After a lot of research, I came to the conclusion that my issue was the commanded idle RPM was too low. Using an SCT X3 and LiveLink, I found out that the desired RPM was a low 560RPM. When I touched the gas or turned on the AC (commanded RPM with the AC on was 590), the idle was glass smooth. I tried to use an X3 to raise the idle RPM, but I had a "CHECK ENGINE THRTTLE CNTRL" error message when I uploaded the tune. SCT was no help resolving the error, so I went to a local Ford dealer.

I first approached them by simply asking them to raise idle RPM to ~650 and they were open to that. Since they were open to computer recalibration, I brought up the point of an updated calibration dealing with the rough idle. There is an updated calibration and I tried it out.

Turns out that the new calibration works. Commanded RPM in drive under closed loop is now 640rpm and my EB runs very smooth.

So to those with a rough idle problem that is not caused by a mechanical issue (ie bad plugs, coil, coil boots, vacuum leak, IAC - Idle Air Control solenoid, etc), check with your local Ford dealership. It should cost you about 1-hour of labor, or ~$100. Best money I spent.

Hope this helps others.

 

From what you are saying it sounds like your problem could be caused by a couple of things. The first thing I would check is the injectors. Buy some injector cleaner, I think the best one is Techron Plus, it cleans the entire fuel system and it has fixed some cars of mine in the past with dirty injectors, I would do this first just because it is the easiest thing to try and it wont hurt anything. If the problem still continues then I would look at the ignition system. It could have a bad COP or plug which would cause a rough idle. If you wont to test if it has a misfire, start the truck and get it to operating temperature and then come to a stop and brake torque the engine, if it doesn't misfire under load then I doubt that its a misfire. The next thing that I would check is a couple different sensors. I would check the IAC, idle air control, MAF, mass air flow sensor, IAT, intake air temperature sensor. I doubt that this would be causing the problem because it would set a code and the check engine light is on. The final thing I would check would be a vacuum leak. Again I doubt that this is causing your problem because it would set a code because the engine would think its running lean and the fuel trim would be off, it could be a very small leak but still cause the symptoms you described. My money would be on either the fuel system or the ignition. I could be something else but this is what I have seen most if the time.