Vehicle is a '99 F150, 5.4L with 90K miles. Located in Central TX.

Background on the problem, I'll try to be brief: Apprx. 2 yrs. ago, fuel pump went south, had pump and check valve replaced. Fuel filter had been replaced not long prior to that. Sometime shortly after that I began getting a funky idle condition under specific conditions, i.e. winter-time or early spring, warmer than normal day (70F or above), hot-soak for 5 - 20 minutes. Barely idles, up-and-down on the rpms, but after approx. 1 min. it runs OK. Have not had a problem during colder weather, NOR during the summer (90 - 105F). Seemed to me that for some reason the winter blend on a hot day gave trouble. No MIL, no codes show up.

This week we had a day with temps up to 81F, and it did the same thing, BUT after a few errand stops, it started hiccuping while I was driving. This steadily progressed to being almost undriveable, like turning a switch off and on - surges, then almost dies, surges, almost dies. Load conditions don't seem to matter, as it will do it on a downhill coast. Had to limp home in "2" keeping rpms around 3K. Lumpy idle would not clear up either.

Next AM, it was much colder (40F), and it started and idled normally. I have not needed to take it out since, so I don't know what will happen once it warms up.

This time the MIL lit up, and it tells me there's a lean condition on both bank 1 and bank 2. The freeze-frame was taken at idle, and shows a short-term fuel trim of -18.75 on both banks, but a LTFT of +25 on both banks.

This leads one to think there is a severe vacuum leak of some sort, or a fuel delivery problem. I've inspected the hoses I can see, but all seem OK. MAF was cleaned not long ago as routine maintenance. Pulled the vacuum hose from the FPR, and it was dry, no sign of diaphragm leakage. (I know that's not definitive, but I'd think with this severe problem it would show up.)

From what I've seen on other sites, the 5.4L commonly has a problem with the PCV elbow connex on the back of the intake manifold, and also has a common issue with the MAF, as well as intake manifold leaks.

I could see the MAF being suspect if it were just running badly, but still drivable, and same with the intake manifold. The PCV elbow is a good possibility, but there's a lot of work involved to just "take a look". As far as I can feel it, it does not seem broken off, at least.

So, I'm looking for suggestions as to what to immediately check the next time it goes wonky. (Warm weather predicted for next week.) I know I can unplug the MAF to see if it clears the lumpy idle, but what else should I suspect or test at the time?

Thanks!

 

If you have or recorded any DTC's those would in infinitely helpful here...

The PCV tubing elbow you mention is almost the first culprit when the Lean Bank's 1 & 2 is noted. Regardless how much effort it takes inspecting and/or replacing that fitting is vital to beginning to solve your issues.

If your engine has an IAC and its defective or has failed that too should trigger a DTC however that's not always the case, still a big possibility.

Let us know the results of checking the PCV elbow.

 

The DTCs are the usual P0171 & P0174, no other codes triggered. I'll start digging into the PCV connex, thanks. The IAC is in the same area so that can be at least cleaned at the same time.

 

Today I pulled the throttle body off to inspect the PCV line. There was nothing visually wrong with the fitting at the back of the intake manifold - it was still flexible and functional , but given the time involved in getting to it, I picked up and installed a new assembly from the dealer. Found 3 other vacuum lines that were deteriorating, and, while none of them were cracked or obviously leaking, I replaced all that were flaking.

I've also checked the resistance on the intake air temp sensor and it is reacting to varying air temps as designed.

Given that there don't seem to be any major vacuum leaks, I have to conclude that some component is failing. I'll check the voltage readings on the MAF, and also fuel pressure when it is back together & running.

While I have the throttle body off, I'll also clean out the IAC valve and check it per the Haynes procedure.

Any other ideas??

Still scratching my head. . .

 

Throttle body, hoses, etc. back in place. Truck starts and idles just great at this point. Next I moved on to utilize my newly-purchased fuel pressure gauge, but ran into somewhat of a quandary: At idle (engine warm fwiw), pressure indicates 31psi. This is on the low end, as specs say 28 - 40psi is the range for this vehicle. Disconnecting the vacuum hose from the regulator brings the pressure up to about 42psi, as expected.

The puzzle is, if I shut off the engine with the vacuum hose connected to the FPR, the pressure immediately drops like a rock to zero; if I shut off the engine with the vacuum hose DISconnected, the pressure remains at about 40psi for at least 5 minutes.

The Haynes manual is unclear as to under which condition the reading should be taken.

So, what have i learned?? Is there an internal leak or is this normal behavior? I've read that a symptom of an internal leak is hard starting/long cranks, but I don't have that problem.

(Further, I connected a vacuum pump to the FPR and tested with the engine running: Result, higher vacuum = lower fuel pressure, as designed.)

 

When you shut the engine off and FP drops have you tried immediately turning the ignition switch back on to check for residual FP maintained in the lines?

Does the truck start, idle and drive as normal?

Unfortunately I can't offer anything helpful past this and don't want to misdirect your process here. I will say Haynes and Chilton manuals typically aren't very helpful when getting into diagnostic procedures such as this.

Best of luck---hope its nothing serious.

 

I just started getting these two codes as well, but my truck is running and idling just fine. I replaced the cyl-1 coil pack a few weeks ago, but it's been running great since then.

Edit: after a bit of research, it appears that my MAF sensor may need cleaning.

 

From my research also, I have seen that is a possible trigger for the lean codes. I've cleaned mine a couple of times very recently, but it made no diff in the hot-soak-idle problem.

As it happens, I was doing some electrical checks on my MAF today, and it appears that there is an open circuit across the signal and ground pin sockets, which - if true - would mean a bad MAF. Not unheard-of on these trucks. Need to do further checking; I don't know if it is possible for that condition to exist on my engine and not throw a code.

 

@ sundvl76, My 04 5.4L 3v recently had a similar problem - only in the reverse - at low temperatures <35º. I suspected with mine (as I suspect with yours) that the PCM is receiving "bum" temperature, barometric pressure, or air flow sensor signals that are causing it to "foobar" settings such as STFT or LTFT / advance / timing / actual throttle position or IMRC valve settings. LTFT was +25 on both banks at idle, and +10 to 20 driving.
I flushed coolant system real well, replaced thermostat (w/ 195º) and put in 50/50 coolant. Things improved some, engine warm-up and closed-loop operation occurred more promptly, but no joy with junky idle at cold startup.

I noticed "intake air temp" reading (from TORQUE APP) was considerably higher at startup than dashboard "outside temp" reading. It would track upward from there, often running 30-40º above ambient. I found that mine (I don't know about yours) doesn't have a separate Intake Air Temp sensor. Mine has the IAT sensor built into and part of the MAF, so I paid $285.00 for a new one (a FORD dealer part). That SOB produced readings on the Torque App that were WORSE than the original - but still higher than ambient. I also noticed "Mass Air Flow" readings on the new MAF tracked generally lower (29-30 CFM @ 600 RPM idle) than the original one (32-35 CFM @ 600 RPM idle). The problem was WORSE with the new MAF - and there were even more new negative symptoms.
I could not find out from ANYONE what normal readings should be, and finding that the damn FORD part was non-returnable, I sprang for another new MAF sensor from NAPA Auto Parts. Immediately - intake air temp matched dashboard outside air temp upon startup, and when driving. At warm start or in start/stop city driving - IAT runs understandably 10-30º above ambient, but will come down to ambient at freeway speeds. And MAF readings on this MAF sensor reads higher (49 to 52 CFM @ 600 RPM). Idle was immediately "better".
It took several drive cycles for fuel trim readings to settle down, but Idle has smoothed out and returned to normal. Mileage is also increasing. IMHO, the 195º thermostat, system flush, clean coolant, and a GOOD (whatever that means) new MAF sensor was the fix for my poor idle at cold startup.
Your situation seems similar. But with added symptom "System too Lean Bank 2". That sounds like a vacuum leak. Sounds like you have the ability to get OBDII readings. I would recommend spraying carb cleaner or starting fluid around on / under the intake manifold - while monitoring O2 graphs, or idle speed - looking for any vacuum leaks.

 

I would bet contacting your stealership's parts manager about what is a defective part might get you a refund----take your documentation or print outs if at all possible. For that much money I'd be hot as hell......

If the stealership won't budge contact the Ford factory help women who post here. Not sure if this is in their wheelhouse but so far they've been great about helping FTE members.

 

The '99 does have a separate IAT sensor. The best I could do was to attach an ohmmeter to it and observe the change in resistance as warm air (from a heatgun) was blown across it. It seemed to behave as expected, although that does not rule out the possibility that it is sending inaccurate info to the PCM.

I actually was getting a lean reading on both banks. Fuel trims for both were the same. That doesn't rule out a leak in the intake manifold area, but the spray test so far has not revealed one, and from what I've read, it is less likely when both banks are reading lean since an IM leak would be probably be on one side or the other.

That surging while driving, and the MIL indicating the lean condition was a one-time occurrence - I've been having the wintertime/hot soak/hot-idle problem for a couple of years with no codes ever thrown. It could be that the condition causing it is getting worse, however I did have occasion to drive the truck on a warmer (74F) day last week and while it did the usual bad idle trick right on cue when the temp passed ~70F, I didn't get the surging at driving speeds and no codes appeared. One test I can do but haven't is to unplug the MAF when it is misbehaving. (It's also very possible that I'm dealing with two problems simultaneously. . .)

My OBDII reader, unfortunately, does not have the ability to give me "live" data, so I am currently waiting for another day with the right conditions AND when my nearby shop can get it in, to get a comprehensive live reading. Based on your experience and my suspicions, I'll get them to look specifically at the IAT sensor accuracy.

Thanks for the post!

 

@ sundvl76;
I like the heatgun idea. I am a believer in "challanging" sensors to observe the response for trouble shooting purposes. I'm always looking for new and cleaver ideas to accomplish that with different sensors (once you can find them - lol). Have you tried using the heatgun on the IAT while at idle? That could prove interesting if you could cause the idle to go stupid.
I would be completely lost if I didn't have "live" readings. I'm not here to preach or promote products - but my "HHOBD", Bluetooth OBDII Adapter from Ebay and the "Torque Pro" app are lifesavers. The adapter was only $27 bucks and the app was $4.95. We spend more than that on one unnecessary sensor! Without them I'm sure I'd still have half the problems with my truck.
The display screens are customizable and you can set up/arrange guages and connect them to whatever OBD signals you want. You can graph the O2 sensors signals! It has an unbelievable list of setup options ---- You can even make the displays "inverse" for "head-up" display, lay your phone on your dash and see the guages in your windshield while driving!! That actually has some application on these Fords that have factory paramaters set so wide they won't set error codes.








Temps screen




Upstream O2's & corresponding Fuel Trims




Corresponding Upstream/Downstream O2 signals at idle

 

I didn't, but that is an idea to try if I could figure out how to get the heat flow to reach the IAT sensor with all of the ducting in place. Maybe just disconnecting at the filter and removing the filter will do it - I'll look.


Wow - holy crap, Buck Rogers! Guess it is time for me to move into the 21st century. . . I'd seen references to BT-connected readers/analyzers, but didn't investigate. I'll definitely look into your suggestion - thanks! Linking that to my Google tablet would give me a pretty trick tool.

In truth, I'm not all that far behind: Probably 15 years ago I invested in OBDII software and a link for a laptop, which worked well - when it worked. Seems as though with each different vehicle I needed to use it on, I had to spring for a "software upgrade", so I finally just quit using it. Plus you pretty much had to be an electronics tech to understand it's terminology (frustrating for a child of carbureted times). This appears to be much more straightforward.

 

I've heard OBD-II codes past 2008 are "universal" across that strategy method which hopefully means all the required software updates ($$$$) will no longer be necessary.

Well that is until the manufacturers find another way to charge for such knowledge.

 

On your suggestion, I ordered the HHOBD plug-in and bought the app for my tablet. The adapter arrived yesterday, and I had a chance to play with it today. After spending some time with it, and running thru the "tests" section, I found that the mode $06 was showing a "fail" for TID $41 and CID $12. After some searching on the 'net, I did find that these codes relate to the DPFE for the EGR. It could be a cracked hose, or the DPFE may be bad - one poster mentioned that these are failure-prone for vehicles which use them. At any rate, if this is what's causing my basic problem, this was a very simple way to trace down a non-MIL issue. Should be able to replace it Monday if I don't find a bad hose, and I'll know in a couple of days whether it solves the problem. (Still need to address the fuel pressure question, of course.)

Thanks again - you helped me a bunch.