Like many others before me, I'm experiencing an elusive rough idle problem in my 2007 5.4 3V with 124K. The issue has been happening for about the last 6 months. At idle, every few seconds, the engine speed drops from about 550 rpm to 500 or so (as indicated on the tach), and the truck shakes moderately. One other thing I've noticed is that every once in a while, at higher speeds, if I let off the gas, the truck shakes a bit for about a second, very much like I'm driving over a rumble strip.

The truck runs fine at higher RPMs, though I do not get good mileage, ~12 mpg combined. I believe my mileage was better before this issue popped up. I do not have a programmer/tuner, so I don't know any way to adjust the idle speed.

I do not get a CEL or any DTC codes, which is why it's so frustrating. I've read many threads on the forums, and there appear to be a multitude of causes. I'm hoping the community here can help me narrow down the cause.


Things I've done so far:

• Cleaned MAF & throttle body with appropriate CRC cleaners
• Replaced air filter (stock)
• Replaced fuel filter (Motorcraft FG-1083)
• Original plugs were changed at 90K, replaced with Champion 7989 (I know...)
• After the rough idle started, I replaced the stock COPs with Accel SuperCoils and changed the Champion plugs to Motorcraft SP-515s. It didn't help.
• Replaced Accel COPs with original Motorcraft COPs (I kept the old ones). One had broken the connector, so I replaced it with a new Motorcraft COP.
• Replaced FPDM with Dorman 590-001
• Tried to reset the TPS using the key/throttle sequence. No improvement was observed.

Things I'm considering might be the cause:

• Leaky fuel injector
• Vacuum leak
• VCT issue, may try heavier oil. I've used Mobil 1 5W20 exclusively since I bought it with 50K miles, change every 5K.
• Fuel pump
• TPS bad or out of adjustment
• Other ignition issue, perhaps a COP wire

Any thoughts or suggestions? Any help is very much appreciated.

 

Have you tried to run some Techron fuel system cleaner thru your tank?

You might have a trace amount of water in your tank too.

I'd run some Techron and some Heet.

I get this problem on my Jeep Compass where the engine speed at idle would suddenly drop to ~500 rpm and shake. I notice this in the spring and late fall when the temperatures start changing dramatically from night and day. I run a tank of Heet and Techron thru it, and the problem goes away until usually the next season change. It's done this for about 5 years now. No CELs no abnormal performance issues, and getting the same gas mileage when it has 3 miles on it from the show room. Right now it's got 127k on it and climbing.

 

I haven't tried Techron, but I did try some Lucas fuel system cleaner. Does Techron do anything Lucas doesn't?

 

Sounds like you already know what you're doing.
If it's not giving you any codes all you can do is go back to whatever trusted diagnostics you prefer.
To me, it sounds like a single failing cylinder. Spark, air, fuel. I'd pull the sparkplugs and see if 1 of them looks different from the rest. This will at least tell you what cylinder you are having problems with. And if you have an old Haynes manual the guide to reading plugs is printed, or you can google it for an internet picture.
If you think it's a vacuum leak, you can find out pretty fast with a can of starter fluid or carb cleaner. Quick bursts along all the areas with vacuum lines, then where the intake meets the heads. Listen for the idle to climb a couple hundred RPM, it's very noticeable.

Sorry, that's as much help as I can give.

 

Sounds like you tried a good amount of things with no luck.

If this was my situation personally, I would take it to the dealer and see what they say. At least they could diagnose it for you and tell you "you have to replace X" and if you want take it back and fix it yourself, you may just have to pay diagnostics services.

I've done this with my wife's Terrain, rear camera stopped working, didn't know if it was the actual camera or the mirror where the display was. Took it to the dealer, they swapped out the mirror and troubleshot it to the camera (for free). Then I took the car back and changed the camera myself.

Brian

 

may have a vac leak somewhere, try spraying around w/ carb cleaner, see if rpm changes. don't go heaver on the oil, MPG will drop. hook up a vac gauge will tell ya a lot too.

 

Not intending to hijack your thread but I have the exact same issue with my 06 5.4l 99k miles. Plugs were replaced by previous owner (at shop) around 70k. About 9 months ago I got a misfire CEL on cylinder 4 (I have true dual exhaust and you could hear misfire from passenger side pipe). I swapped COPs on 4 and 5 hoping to verify it was a spark issue and the issue went away completely until about a month ago. Now it is getting progressively worse, but with no CEL. Same exact symptoms as yours (intermittent misfire at idle, when coasting, and dramatic fuel mileage drop) and the misfire can be heard from passenger side pipe yet again, making me think it is not a COP failure. I am thinking of taking it to be diagnosed by shop, I will let you know what I find.

 

Sometimes switching COPs may fix it for a little bit, if the boot is damaged or a carbon track on it can cause a miss fire shorting from the boot to the inner wall of the spark plug channel/tube. This may not set a code because the spark is still firing most of the time. Coils could be starting to go bad too.

 

Okay so first some background on my pickup. Plugs were replaced by a shop around 50-60k.

Started getting CEL (finally). It was P0300 and P0304. So I pulled the plug from #4 tonight and the entire "interior" part is covered in a wet/burnt oily residue. The threads were also chock full of debris, making backing the plug out a pain. Nervous about putting new plug in because as soon as the threads grab its very hard turning. Pulling the new plug out after about a quarter turn the sleeve is covered in residue and the threads are full of crap like the old one.

What I'm figuring is oil in cylinder = my misfire at idle issue? Am I looking at bad piston rings? I have yet to pull other spark plugs because I'm scared they will be a pain to reinstall like #4.

OP have you checked your new Champion plugs to see if you have similar oily residue?

 

An update on my rough idle/misfire: I don't know if the problem was a bad plug or a bad COP boot, but I replaced both (Motorcraft SP-515 plugs & Belden 702460 boots), and now my truck idles perfectly. I applied nickel anti-seize on the plugs per the TSB.

Spoiler222: I once had a misfire like yours that threw a P0303 code. The problem at that time turned out to be a leaky fuel injector. I installed a new Motorcraft CM5144 injector from Amazon, and that fixed my problem. The other problem was that the leak also wiped out my right side O2 sensors, so I ended up replacing all 4 with new Bosch sensors.

I replaced my Champion plugs after about 30K on them, because I wasn't happy with them. I did not observe the oily issues you seem to have. One piece of advice, blow out the spark plug recesses with compressed air before removing the spark plug. That will remove the dirt so that it can't get into the combustion chamber.

 

You also have to replace the boots when switching back and forth from Motorcraft and Champion plugs. If you don't you won't get a good seal.