Codes p0171 and p0174

[Ldub]

Just cleared out my 171 and 174 codes this weekend. An intake tear down and a solid blast of MAF cleaner did the trick. Did not bother with the o2 sensors. I just passed emissions about 3 weeks ago (CEL didnt spawn until 2 days after I passed, heh), so I am in no immediate hurry. I will just wait and see if the sensors themselves decide to throw a CEL (I believe that is a 420 if I am not mistaken).

Thought this may be related at first since both popped up about the same time, but it does not appear so. Even after cleaning the MAF and clearing the codes, my VX is still running.... funky. On cold startup, it idles at roughly 2k-2300k. On warm startup, sometimes it simply stalls at idle unless given some juice. This is all new as the S/C has been in for almost 2 years now. I am leaning towards the FPR and/or the EGR. Both were fully prepped and cleaned when I installed my S/C, but considering I have 7 hard years on both, it wouldn't hurt to replace. It may also be one of the reasons why the VX has started to run a bit lean and is suffering minor fuel dump. Thoughts?

FPR could be a contributing factor, especially if you didn't pop in a new one when you installed the S-C. BTW, you can get a right angle snap ring pliers that JUST has enough clearance, at Harbor Freight for cheap...
The one I got has straight, 45 deg. & 90 deg. interchangable jaws.
Also, the snap ring that comes with a new FPR is too small for the aluminium block on the S-C kit, so re-use the old one.
The lean condition that the codes are indicating, from my past experience, points towards a vacuum leak, either intake gaskets or vac. line.
I've had vac. lines pop off under boost, also check the PCV valve & hose, I recently had the same exact symptoms & it turned out that I had a bad PCV valve. (the top & bottom had come apart)

[WormGod]

I replaced the PCV a few months ago, as well as my temp sensor, so I think those should be good to go. All vacuum lines were pretty solid though I was skeptical of my plumbing for my CAI. I removed all of it up to throttle body and replaced it with the OEM air box, for now anyways. I thin kI am gonna do this in increments and get a new FPR first and see how that goes. I didn't replace it with my S/C install, so I don't imagine it would be a bad option.... except on my wallet in this lovely !@#$ing economic doomsday.

And speaking of which, going back to the air box, my ScanGauge relays that my fAI is about 20f cooler than it was with my CAI plumbed into the fender port. Some food for thought and means I am gonna have to, once again, head back to the drawing board. Not at all what I was expecting.

[WormGod]

Dag nebbit! CELs came back today after a stall just after startup. *sigh*

First it threw the 174 and then the 171. Looks like I am gonna go the o2 sensors route now. See if I can hunt down some bargains....

[VehiGAZ]

Gary, for what it's worth, I suggest you try a new MAF first instead of O2 sensors. Cleaning an MAF can help if you run a K&N, which will muck it up sooner or later, but MAFs just go after a while, in which case cleaning won't help. Your symptoms are consistent with the ones I had with a bad MAF last winter.

[WormGod]

Wallet allowing, I have a few things planned in the near future so that I can hopefully avoid any later issues.

Looking at replacing the o2 sensors, fuel pressure regulator, EGR, and I will take your advice on the MAF into consideration. I lost $8k in the last 3 months in the stock market so I am gonna be watching my spending a bit more closely so I can keep my nest egg secured.

[taylorRichie]

Just tripped the two codes on the way to the office this morning.

Based on this thread I'm thinking I should clean the MAF and see if that does the trick.

If it doesn't work out then, 02 sensors, FPR, and EGR? What about a PCV clean or replace?

Suggestions?

I'm only at ~52,000 miles. Also this is the first tank of gas I went with 85 octane instead of the normal 88 or 91, could the octane change cause a lean condition?

Thanks guys!

Richie

Glad I did the search and found this wonderful thread.

[tom4bren]

"could the octane change cause a lean condition?"

I'd say no but then everyone would beat me up so I won't.

I've always operated on the KISS principle when tracking down problems. Clean the MAS & reset the 'puter. If codes come back, try going back to higher octane & throwing in some gas treatment. If codes are still there, move onto FPR then EGR then O2.