I could use some help trying figure out my problems with my truck.

2003 F150 FX4, 4.6 EFI, manual transmission. 167,000 miles

My truck threw the above codes. The symptoms were a high idle, 2,500 rpm, when coming to a stop with clutch in, after a few seconds the idle will come down to 700 rpm but feels like there's a misfire.

First I changed out all four oxygen sensors and that didn't cure the problem.
Yesterday I changed out the mass air flow sensor and that didn't correct the issue but did help somewhat.

The code reader did say there was a misfire but didn't state any particular cylinder, so I don't think it's a coil pack, and there was a lean fuel mixture present.

The guy at Autozone said it could be the throttle body. I plan on buying some cleaner and trying that.

I don't think it's a clogged fuel injector but I could be wrong.
Is there a fuel regulator sensor? Perhaps a clogged fuel filter?

So I'm scratching my head trying to figure out what might be the culprit. I've spent &325 on parts so far and really don't want to take it to a shop.

Any suggestions would be appreciated.

 

Same as the last thousand or so threads with the same code pair.

Vacuum leak in 95+% of the cases. Might be a MAF sensor (sometimes).

NEVER an O2 sensor problem.

 

YEP... vacuum leak. Look at the 1/4 inch vacuum hoses off the intake manifold. My 5.4 had two old , hard, cracked hoses above the drivers valve cover to the EGR stuff. That set off both codes.

 

Look into replace the intake manifold gaskets. I have the 4.2L V6 and replacing the gaskets plus the isolator bolts fixed it right up.

 

He's got a 4.6, not a 4.2.

 

Thanks for your inputs but I don't believe it's a vacuum leak. I've checked all of the vacuum lines and they seem to be in fine shape.

Here's a list of what I've replaced and the problem is still occurring.

- All four oxygen sensors
- Mass airflow sensor
-Idle air control valve

Now I'm wondering if it could be the fuel pressure regulator or maybe the EGR valve.

My truck has a 167,000 miles on the clock so I'm actually not angry about replacing the items above, the way I see it they were going to need replacing sooner or later. I am getting a little frustrated that I haven't solved this issue yet.

I'm scheduled to have new tires installed tomorrow and I'm going to have them diagnose test it to hopefully find out what is causing my problems.

Any suggestions?

 

when was the last time the air filter was replaced or cleaned. Clogged air filters can cause this issue. Vacuum lines can look ok but still deteriorate from the inside out as well, So I'd replace those if they haven't already been done recently. Don't use a throttle body cleaner on your throttle body as these on are coated and even the "special cleaners" can ruin the coating. Then if that doesn't fix the issues you are having test the injectors. Also how long has it been since the fuel filter has been changed?

 

Air filter was cleaned and oiled yesterday. Wasn't that dirty but I thought since I was already wrenching my as well clean that too.

I have replaced the fuel filter but that was probably 75,000 miles ago...in that ball park.

None of the vacuum lines are hard or brittle, all connections seem to be fine.

 

Ok when you touch the vacuum lines do they leave your hands very black and sooty like? If so they need replaced. What happens is they can be soft but not to soft just like new. But when you touch them or as they vibrate while the truck is running the rubber starts to fall apart. And although they look and feel ok, there are actually tiny microscopic hole opening up allowing unmeasured air to get into the engine causing drivability issues. And like I stated before they can and do deteriorate from the inside out as well. If they are original they need to be replaced. At 167,000 miles they are way over do.

 

Okay, the vacuum line coming out of the booster drum (?) that goes into the back of the throttle bottle is very suspect. Do you recommend getting the OEM replacements hoses for the preformed vacuum lines?

I went ahead and picked up a new fuel filter at NAPA. I imagine it's over due too.

 

Quit throwin' parts at it (after replacing the fuel filter)!

Did you say "oiled filter"? If so, clean MAF sensor elements, reset the PCM, put in a PAPER filter, and start over from scratch. Over-oiling is common and the oil can contaminate the MAF sensor wires.


Otherwise, check for a vacuum leak as follows:

Hook up a scan tool and look at your two short term fuel trims. While monitoring them in real time, use judicious shots of a flammable (brake cleaner, carb cleaner, ether, propane, etc) at suspect areas, avoiding the air intake to the air filter. Do NOT burn your truck and garage down, do this outside! When the flammable gets sucked in through the leak, you'll see a spike in one or both of the trims that may take as long as 30 seconds to settle out. You probably will never notice any change in engine operation. You can quickly find any vacuum leak this way.

 

Okay, I replaced four vacuum lines. Two that come out of the brake booster drum (whatever you call that big round thing) and two smaller ones that go into the EGR valve. It really helped matters a lot but the problem still present but not as bad. Maybe I'm missing a few other vacuum lines? The two vacuum tubes that come out of the valve covers seem to be hard plastic tubes so I didn't think they could be the problem, but maybe I'm wrong.

The truck is really running great under a load but once you push the clutch in it idles high momentary and still idling rough in park like it has a misfire.

I have thrown a lot of money towards trying to solve this problem but I think it's worth it. Everything I've replaced was going to need replacement sooner or later at the mileage I currently have. And since I've replaced all of these items on my own I've saved a ton in labor cost. A local service station wanted $650 to replace all four 02 sensors. Well that was $450 in labor I saved.

In a couple of hours I'm getting new tires installed and while I'm there I'm going have them hook it to their diagnostic machine. I was hoping to figure this out on my own but it's time to pay someone to tell me exactly what the culprit is. Could be as simple as a clogged fuel filter...I guess maybe.

I'll definitely chime in again and give a up date later today.
Let's hope it's a simple and cheap fix.

 

I've noted that on manual transmission trucks this specific fault is reported quite often and difficult to pin down.
Idle out of control and engine stall related to clutch operation.
This is a situation unique to manual that auto trans does not have very often.
Check out the rear of the intake manifold for hose hardware needing attention.
Here is what is supposed to happen on deceleration in and out of gear.
On decell in gear, the PCM gets vehicle speed input telling it the speed is decreasing.
At the same time the TPS is closed down by release of throttle position.
The combination of these two causes the IAC to close down to just pass enough air to keep the engine from stalling as well as close down fuel injection to a low amount.
At very low speed the IAC and fuel injection retakes control of the idle as it normally must do.
.
These actions are not happening for some reason when the clutch is in and it's off normal signal interrupts the signal path. Auto trans does not have the clutch path to deal with nor down shift the transmission.
The IAC is not recovering the idle air and fuel may not be recovering causing the stall.
.
Carefully look and check for air leaks in other places because the PCM detects this as the cause by the codes set, indicating the fuel tables have shifted due to the excess air.
It's a round about way that exhibits itself in codes 'and' drivability issues on a manual trans truck..
Good luck.

 

Thanks Bluegrass and everyone else for their inputs. I hope this is the cause because vacuum are heck of a lot inexpensive than other parts to replace.

Will report back later today.

 

jd, not to pick on you, but the first thing you need to do is slow down, look at the problems, and figure out what is causing them. IF you dont know, get the codes and ask here. 171 and 174 are VAcuum Problems 90% of the time. THe O2 sensor and MASS sensors are not the first place to look. My 2001 had 235K miles on it, 12 years old, and original sensors. They can go bad, but those codes should be vacuum related.