Sorry to beat a dead horse... codes 171 and 174

[s.eich]

Did a bit of searching on this issue, but came up with so much I'm not really sure where to start...

'99 Explorer Sport, 2wd, 4.0 SOHC, 85K miles

Pulling engine codes: 171 and 174, Bank 1/2 too lean

Problem: Engine won't idle on start-up, 90% of the time. Seems to help a bit if it is in the garage vs. outside, and maybe a bit when it is a little cooler. Engine will start, idle at 1500+ for a few sec, then drop below 500 and die. Will do this repeatedly unless you rev it a bit. Problem always occurs, regardless if it is first thing in the morning, or after driving it around (warm) and restarting it. It has even got to the point of dying when it is put into Park.

Just replaced the o2 sensors before the cats per Autozone's advice , and what the manual appeared to be pointing to, but to no avail. Looks like I'm not the first, though.

After searching, looks like a lot of ppl are pointing to a Ford recall M00112 or similar, upper and lower (manifold?) o-rings and a tensioner. Other possibilities... EGR valve, DMFE (or something like that, lol), vacuum leak, dirty MAF or throttle body.

After dropping $120+ to replace prefectly fine o2 sensors, I don't feel like chasing a bunch more gremlins to no avail. Any advice on the specific cause would be appreciated. Again, looks like everybody is pointing to the o-rings, but a few said it would improve once the engine warmed up (which mine doesn't... performs exactly the same warm) and the rings expanded, so I'm not sure what exactly to think.

Thanks for the help. -Steve

 

[jah81592]

PO171&174 ARE LEAN CODES. I would look at my intake tract and make sure no hoses have slipped off between your MAF and t/b,also make sure that your hose (if stock) has no tears,cracks or etc. If all is well then I would look toward the intake manifold gaskets for leaks. Lastly test your MAF, had one come to my shop and the MAF was bad the strange thing it never threw a MAF code just 171&174 and wouldn't idle cold or warm. But in your case I would first look toward vac leaks,vac hoses and such. That code tell me that there is unmetered air going into the motor and the computer cant adjust the A/F ratio. If you have anymore questions. PM me.
If all vac hoses check out I would lean toward the intake manifold gaskets(orings). They are cheap. FelPro's found at Advance Auto pt#MS90890 and list for $18.48 a set.The oem's are known to harden and loose their seal!

 

[s.eich]

Thanks, jah; I'll be looking into it this weekend. I hate all those stupid vacuum lines, and there are so many sensors to try and mess with it's nuts. Sounds like the MAF sensor is pretty uncommon to replace, though, huh?

Anybody have a write-up on replacing the o-rings? Pictures would sure be helpful, and the manuals seem to be useless (all the pics appear to be for a different motor). Just hate to dive into a newer motor blind... so dang finicky with all the FI and everything being computer controlled anymore. -Steve

 

[Trailbum]

There IS a very detailed post somewhere on this site.... Don't know exactly where I found it, but it was complete step by step with photos!! I printed it out and used it for reference as I did the O-rings on my 2000 Sport 4.0!! It was actually a pretty easy job and only took a few hours. What a feeling to fire it up after putting it all back together, and hear it idling perfectly!!!

OK... here it is!!! Hope the link works for you. Read post #33!!!
http://www.explorerforum.com/forums...ight=oom12+ford

Dammit... The link doesn't work!! OK, bear with me here...
Do a *search* on "00m12" You will get many pages of results.. Go to page 5 and look for a post titled "98 SOHC COLD START IDLE PROBLEM" (that post is 5 pgs long). Go to post #33 and it is the step by step with photos.. very helpful. Good luck, it's actually pretty easy!!

 

[s.eich]

Thanks, trail; I'll check into that when I get a sec. Sounds liek exactly what I was looking for. I love forums. -Steve

 

[iturama]

171 & 174 codes

I pulled 171 & 174 codes off my wife's Explorer. She reported a bang from under the hood, smoke and the smell of burning. When I looked, I couldn't see any sign of burning nor smell. I did notice that the clasp on the air cleaner housing was unbuckled. Checked the air filter and it was clean except for a small oil/soot stain. Noticed a fine layer of dust around the place. When I turned the engine on it fired up Ok but it was running irregular - slowing down to idle and then running up to 1500 rpm. At low revs in drive or reverse it felt jerky. In park, the revs would pick up again.
Decided to add some injector/valve cleaner and take it for a run. It was then I had a CEL and pulled the codes.
Anyhow turned out to be vacuum line that had blown off near the air intake. Now running perfectly. Moral is check the simple things first.
I can only assume the engine blew back. Would explain the stain in the airfilter and dust. Apart from running the cleaner fluid, the only other thing I have done is change all the spark plugs.