catengi

Greetings all! This is my first post here so hopefully I've put it in the right spot. I know there are tons of threads on here about these trucks having a rough idle but unfortunately I haven't found anything like my case. I bought the truck used from a private party about 3 weeks ago. It's a 2004 F150 Lariat with the 5.4L and 145,000 miles. I find that more information is generally better so first I'll run through the problems I'm currently experiencing, and then attempt to give a relatively thorough history of what has happened and what I've done with the vehicle.

When I first start the truck in the morning it runs fine until the coolant has reached normal operating temperature. Once the coolant has warmed up it starts to idle and run pretty rough. At idle it usually hovers around 500rpm and you can feel it shudder through the steering wheel. When you get on the gas it seems to have no power and if you get it in the 1,500-2,000rpm range it will shake the entire truck. When coasting it is less noticeable, but when gassing it attempting to keep speed (around 45-50mph) or accelerating from a stop it shakes like mad. If I turn the truck off and let it sit for 15-30 minutes it goes away and I can drive it the rest of the day with no issue. This does not happen every single day, but 75% of the time I drive to work in the morning.

Alright, so here's what I have done in attempting to diagnose this issue.

Several days after purchasing the truck it began to run rough on my way to work and threw a CEL. I drove it straight to the auto parts store to have the code read and it came back P0420 (Bank 1 Cat system below threshold). Did some research and decided to clean the MAF and throttle body before I pursued a new cat. I also purchased a bluetooth scan tool so I would not have to continue running to the auto parts store to get codes read (best $22 I ever spent).

That evening I cleaned the MAF and throttle body and reset the ECM. I also filled the gas tank and put a bottle of Lucas fuel injector cleaner in the tank. After driving the truck for ~50 miles during the weekend the catalyst system came back complete and has not thrown the P0420 code since. All was well for several days until it started running rough on my way to work again.

Although I was not getting a CEL I decided to check for codes and got P0171 and P0174 (bank 1 and 2 system too lean) as pending faults. I drove the truck for several more days and the codes ended up going away and never threw a CEL. Around this time I discovered I could monitor the total number of misfires I was having using my new bluetooth scanner. I setup my counter and waited for the next morning. Sure enough, it started to idle and run rough and my misfires starting climbing (it counted roughly 750 misfires during the last two minutes of my drive into work). I also managed to catch a pending code for misfire in cylinder 4.

That evening I took the COP and plug out of cylinder 4. I saw no evidence of fluid leaking into the hole but it was rather hard to see back there. I blew the plug off with some light compressed air and reinstalled it. I then swapped the COP on cylinder 4 with the COP on cylinder 1 in hopes of tracking the misfire to either the COP or plug/wiring harness. It is probably good to mention here that the previous owner changed the spark plugs with Motorcraft plugs less than 10,000 miles prior (yes, he did provide the service record for it). Somewhere I have a picture of the plug and hole, if I can find them I'll upload them.

This is where I get lost. After reinstalling the plug and swapping the COPs it ran like a top for several days. Put about 250 miles on it without so much as a hiccup. It started running rough again several days ago but for some reason my scanner is not reading a single misfire. It's happened three times now, and each time my misfire counter doesn't record a single miss.

This is where I'm at right now, honestly not sure where to go from here. Some other things I have noticed which may not have any bearing on the current issue is a faint burning rubber smell when I get out of the truck after driving it for the first time. Again, rather faint but if I stick my head up under the rear driver's side wheel well I can smell it pretty good but it goes away quickly (honestly may be normal, but my old truck never did this). The exhaust has some leaks in it, but as far as I know it's all after the cats (small rust hole in muffler and some shoddy welding on the muffler inlet pipe). Also, for some curious reason the evaporative system still shows as incomplete on my scanner even after ~300 miles driven since I last reset the ECM. I apologize for the long wall of text, but it was the best way I could think of getting all the information out there. I'll update my post if I remember any more pertinent information. I'll gladly take any guidance or advice you guys may have on this issue!

tomb1269

Sounds like you have an issue with cold idle adjustment, i.e. IAC valve but our trucks do not have one as they are electronic throttle bodies. Try taking the throttle body off an cleaning. Check on the site here or on the web for cleaning steps, just do not go crazy with solvents or use any bushes to clean it. Just good quality carb/injection cleaning spray and clean, clean clothes. No gaskets need so the only cost is rags and cleaner. Just make sure to put cloth over intake once throttle body is off to assure no debris get in. Also make sure to tape on sockets, torx bit tips, etc. to extension to assure that you do not drop any in the intake.

Martian

Throttle body cleaner and an old toothbrush. Easy. Just don't clean it while it's ON the manifold. You don't want all that sh*t running down into the engine.

catengi

Thanks for the advice guys. I have cleaned the throttle body once already, but admittedly was unable to get it perfectly clean before I ran out of TB cleaner. I was using a relatively stiff brush to help clean it, but I can see how cloths or a toothbrush would be a much better idea. I'll have to get another bottle of TB cleaner and have another go at it! Any areas in particular I should focus on or just shine it up?