YES!! Another 0171 and 0174 question.

[99xlsdude]

99 XLS V6 OHV 108K miles.

For about a year, off and on I've had 171 and 174. If I unplug the negative battery cable, the codes go away - sometimes for weeks at a time, other times for a day or so. They eventually return but only on a trip when the truck is driven in wet and cooler weather. The codes are set (CE lite turns on) about 5 minutes into trip (around the time the engine warms up).

I searched the forum and did the standard stuff - cleaned MAF, IAC, TB; installed new plugs, wires, air filter, PCV; no apparent vacuum hose leaks. Idle is smooth (approx 700-800 rpm after warmup, 1500-1800 cold), no performance issues - warm or cold. Passed NJ emissions inspection (during a period when CEL was off).

Does this pattern (CE lite turns on only in cool/damp weather and 5 minutes into trip) point towards a specific part or problem? For example, might this indicate a faulty MAF sensor (e.g. excessive condensation)?

Any thoughts?

Thank you very much for your help.

 

[ThePhoenix]

same here....they go away then come back....sometimes a week, sometimes three days...but mine went away when I cleaned the IAC. prior to that, it would always come back the next day. I am leaning towards intake gaskets being the problem. but....I justy dont know

 

[btexpress]

I would think intake gaskets, in colder weather there may be less expansion and contraction of the plastic manifold and/or gaskets. Not uncommon, although much more prevalent on the SOHC motor, the OHV does have intake gasket problems, which are actually o-ring type seals. Before throwing other money at it for sensors or anything else try the intake gaskets.

 

[99xlsdude]

Thanks. I reviewed the post on performing this procedure and it seemed like it was a little beyond my comfort zone. Looks like a visit to the dealer.

Does just tightening the intake manifold nuts ever help?

 

[99xlsdude]

I tightened the intake manifold nuts to 17 ft/lbs over 1 week ago - 3 needed to be tightened including the ones on each end. I reset the CEL and so far it has not returned. I'm keeping my fingers crossed.

 

[ilh]

99xlsdude,

new to the forum maybe, but not new to the explorer and definitely not to the 0171 and 0174 codes!

i've got a story and a solution for you, as my father's ST threw these codes at least 6 times before i finally tracked it down. i cleaned the MAF numerous times with only temporary results, and even tore the engine down to the throttle body to tighten what i thought was a loose sensor. (it wasnt snug, but it didnt make a difference.) i dont remember when i noticed a new, peculiar whistle, but anyways...

after this i started the truck again and began to feel around for loose fittings of any sort. refer to the attached picture, as i present my findings:

i just jacked this off the internet. i believe this was off a mustang. look at what i've highlighted in hot pink: its a hard line on this mustang, but on my ST its a bit different and comes in the form of a rubber 90 degree elbow that goes to the manifold. im pretty sure it has something to do with the PCV system.

at any rate, when i put my hand on this fitting to give it a wiggle, i noticed that my thumb was stopping the whistle! hmm! shut the truck off and pull it off to inspect.

guess what? there were 3 1/4" cracks in the rubber! thus creating a vaccum leak from the PCV, and the residual fuel from that wasnt getting fed. thus, the engine was running lean!

i temporarily fixed it with silicone and electrical tape because my father needed the vehicle the day after for a 4-day trip and by this time all parts stores were closed. it didnt throw a code for 3 weeks, until i was on a family holiday, about 500mi from home...

well to no surprise my repair had gotten mushy and was creating the same leak. we stopped at a local parts store, got a replacement piece of simple rubber hose, and were on our way! when i got home it was the same code so i cleared it and it hasnt done it since (8 months).

this might not be your fix, but i hope it helps!
ian

 

[ThePhoenix]

unfortunetly, its not in the same place on my 2001 4.0 SOHC....

 

[99xlsdude]

ilh (ian)

Thanks for the tip. The PCV hose is in a different place on my engine - near the rear of the intake manifold on the driver's side. I checked this hose when I replaced the PCV valve but I will check it again just to be sure. Thanks again.

 

[ilh]

ThePhoenix,

are you sure? mine's about 2 inches behind the throttle body. its not open in plain view, but there's a hard hose along the engine you can follow. it runs to this elbow and in.

not to say that it isnt possible ford changed something mid-year.
i cant really give you a picture cause im not really at home right now. :

 

[99xlsdude]

CEL returned so I changed the upper manfold gaskets. CEL gone - hopefully for good.

 

[drdoom]

Found something...

I just got my 1997 XLT 4.0 SOHC back on the road after over 4 years. First thing I got were codes 0171 & 0174. Symptoms were just like all the threads I have been reading here: stalling, surging, etc. I tried to find a vacuum leak, and found one at first...a small hard plastic vacuum line was deteriorated. But the problem persisted. I have read a lot here and in my Haynes manual about the IAC valve, intake gaskets, fuel pressure, etc., so today I had a chance to have a closer look. I pulled the plastic cover off of the plenum, to have a look at the IAC, and also whatever the thing is behind it (I knew already the small circlip was missing there). Here is a photo of what I found:

The blue arrow is where I replaced the missing circlip. I picked up a 2 pack at Home Depot for 38 cents.
The red arrow shows where I re-connected the large hose that goes into the IAC port. This was completely disconnected! I believe it was knocked loose when I was working on the valve cover. So far, this seems to have corrected the problem. I cleaned the IAC a bit while I had it out. Also, does anyone know what the device is behind the IAC? Earlier this year, when I was working on the engine, I pulled the plenum cover and it was not connected at all.

PS: IAC gasket was present, but was removed when I took these photos.

 

[2000StreetRod]

Vis

The "thing" aft of the IAC valve is part of the variable intake system (VIS) that was implemented on 1997 and 1998 models. It controls the length of the intake runners in the upper intake manifold. The rod on top connects to a vacuum motor that is activated by a solenoid controlled by the PCM. Around 3,000 rpm the PCM starts changing the length of the intake runners. The change in length is supposed to be complete by 3,500 rpm.

 

[drdoom]

Good info

Thank you, 2000StreetRod. I had no idea what that was.