Let me describe this perplexing issue. I have a speratic rough idle problem. When it happens it's almost like the truck wants to stall. Once going the truck is fine. There has never been any acceleration issuse, but for a short time the truck would kind of lunge off idle. It hasn't done that for quite some time. I've replaced the fuel filter. There are no vaccum leaks that I know of. I've tried higher octane fuel. I've tried injector cleaner for a month. What should the fuel pressure be and what is the test port located? Is the fuel pump in the tank? If so, whats that big log looking thing behind the gas tank that the fuel lines run to? Also, there are no MIL codes...

 

Fuel pressure should be 30 - 45 psi at idle. The typical setup for tee-ing into the fuel system is between the fuel delivery hose and the fuel rail. Yes, the fuel pump is in the tank. It is a pump and level assembly. The "big log" is part of the fuel evap recovery system, best guess.

Good luck

 

Any codes? One of the first diagnostic steps in about every category of problem with driveability recommends a code scan to check for codes. Fuel pump is in tank. Fuel pump control module is external mounted to the crossmember between the frame rails just ahead of the spare tire rearward from the fuel tank. These have been known to corrode thru or rust thru and cause driveability issues. a PO191 code would point me in that direction.

 

me too, any codes?
check spark plug wires
check to see if your MAF is dirty
air intake leaks?

 

There are no codes that I know of. Seems to happen when the motor is warmed up. No spark plug wires, coil on top. Today driving to work there were no issues. Coming home there were no issues until I pulled in front of my house. Then the rough idle started again. A Ford guy I know says it sounds like it might be on/off vacuum leak, which makes sense but I can't hear it. It's like 17 degrees and I have no garage so working under the hood for any amount of time will be short. I have a good scanner that I can do a live data mon so I'm gonna try that and see what happens.

 

Check the IAC valve

 

This sounds alot like what is happening, and it's never been repaired.

Make : FORD Model : F150 Year : 2004
Manufacturer : FORD MOTOR COMPANY
Service Bulletin Num : 05417 Date of Bulletin: MAR 07, 2005
NHTSA Item Number: 10014666
Component: ENGINE AND ENGINE COOLING:EXHAUST SYSTEM:EMISSION CONTROL:GAS RECIRCULATION VALVE [EGR VALVE]
Summary:
INTERMITTENT ROUGH IDLE - NON-COMMANDED EGR [EXHAUST GAS RECIRCULATION VALVE) FLOW. *TT

Where is this? Top of manifold or valve cover? I've replaced them before on my 96 but the 2004 is quite a bit different. On monitor I had a pretty steady fuel pressure psi of 39-40 lbs. It's a start I guess...

 

04+ dont have an IAC valve. its all internal to the electronic throttle body. I had the same problem with my 04.

CLEAN YOUR THROTTLE BODY. i checked everything, and that was it.

my problem was running a K&N filter, oil leaked through and it didnt filter well enough and eventually clogged my throttle body and made it to where the throttle plate tried to stick at idle.

 

I'll try that next, since the EGR replacement was a failure. When you say you had the same problem are you referring to the lunging part? If so, thats no longer an issue. There rough idle is. This truck also gets really poor gas millage when this happens. I do have a decent code scanner thats capable of live monitoring. I'm not sure what mV or mA the o2's in bank 1 and 2 are supposed to be but they go a wide range. Like 0 - 700. Thanks.

 

My rough idle issue took a lot of work to resolve; I tried replacing the plugs and fuel filter. When I started to get codes I swapped the cop's from one side to another to see if it was a bad cop or something else. Turned out to be low compression in #8 due to a bad valve guide seal. Warranty covered a new head and to this day she idles like a dream... Hope this is not the case for you.
Oh, I have a 5.4 3v 04 with under 50,000 when head was replaced...

 

Doubt it's a low compression cylinder since I have no codes showing up. I did a live monitor and everything has checked out OK. I'm using an AutoXray EZ5000. It's a fairly decent scanner. I did notice this today and here's my thoughts. Tell me what you guys think. I was watching the temp gauge. To my knowledge the needle has always been dead center in the middle no matter what the weather or temp out side. It's winter here now so, it takes a while for the temp needle to get to the center of the gauge. When it does and I stop at a light the needle drops a significant amount. then goes back up after driving for a while. This is repeated at every stop. Also, the heater doesn't seem to put out the heat it used to. If this thermostat is sticking open wouldn't this tell the ECM the engine is colder so dump more gas in? That would explain the rough idle at stops and the poor gas mileage when it happens. Let me know what you think...

 

Good question: and I also hope your issue is not low compression. Once you start getting codes they would give you an idea of where to look.
The good news is that a thermostat is a cheap fix...10 or 12 bucks and something you can do yourself. I just replaced one in my wife's car yesterday but her temp gauge laid dead bottom even when driving; luke warm air at best. After new thermostat great heat and you can actually see the temp gauge working... I would certainly give it a try especially since its such a low cost fix. Keep us posted.

 

04XLTRUNNER is on point. My 04 F-150 STX 4.6L just started doing that about a omnth ago, tried all the same stuff. Finally pulled the throttle body and discoverd that my K&N was trying to do me in. I used B12 T/B cleaner and straitend it right out. Havent had any issues since.

 

thank you william. about time someone listened to what i had to say. K&N is a no go for 04+ trucks. these electronic throttle bodys are really touchy to dirt and oil. i had this for almost 6 months before i finally figured out what it was. and i wasnt even looking for it when i found it. i had given up. i was getting ready to make a dyno run at school and was cleaning the intake to make sure i would get the best airflow i could. thats how i ran across it. glad i could be of assistance.

 

I have the exact same issue. 2004 f150 fx4 w/ K&N filter. After the engine warms up and i put it in park, the idle will flucuate and at times the engine will stall. It seems like the throttle body cleaning is the fix? My question is, what is this throttle body and how hard is it to clean? i'm capable of a little more than basic repairs. Could I do it or should I engage my mechanic?

Additionally, the 2004 ford manual stresses not to clean the TB bore & plate because they have a special coating?

thank you all for your time,
rob