tmclem

Hey guys, I've done a lot of research on this but I wanted an opinion on my personal situation before installing something else that has cost me a lot of money on my tight college budget.

So here's my situation:

A few weeks ago, I replaced my serpentine belt and got my oil changed. Immediately after, I noticed my CEL had come on. I brought it to Autozone and was given codes PO171 and PO174 (running lean on banks 1 and 2).

About a week later, my engine developed a rough idle. The truck will stall occasionally at stoplights, and the idle is usually hunting between ~500-1000 rpm. I have to put my truck in neutral at stoplights or in traffic because it is essentially lunging forward and I have to fight it with the brakes. More and more research led me to believe the issue was my IAC. I replaced that the other day, and mine was VERY dirty (since I have 232k miles on the engine, I figured it was worth replacing and not just cleaning). Unfortunately, this did absolutely NOTHING to fix the issue. This was last night.

Today, I took it back to Autozone, to get an updated reading of the codes, post-idle issue. Two new codes popped up, P1131 and P1151 (bank 1 and 2 upstream O2 sensor is indicating lean). I bought the oxygen sensors to replace (pricey for my budget), but am now hesitant to install them. What are the chances that the O2 sensors are actually bad? Isn't it rare that these go bad? And how about BOTH O2 sensors going bad at the same time?

Is there any possibility that the lean condition has caused my O2 sensors to go bad?

Also - the rough idle only seems to be an issue after the engine has warmed up (i.e. if I let the truck sit for a day it takes a little bit for the poor idle to begin).

Thank you for your time and help.

Cmanjr

I just ordered 4 new Bosch O2 sensors off amazon, only $26 per O2 sensor, so my total came to be $112 including tax with free shipping. Should be here next week. But my point is, is that O2 sensors don't break the wallet THAT much. For 2 new O2s you're only paying about $45-$50. That isn't horrible, even on a college budget.

Tackle

You don't need to replace them. Also, because you have both banks lean you need to look at the cause. Something that would effect both sides.

Knowing what engine you have would help.

If the 4.2, the intake manifold causes that issue.

5.4 or 4.6, possibly the pcv itself or the hose it's connected to.

tmclem

Thanks for your reply. That is true, I got the 2 cheapest at Autozone and it came out to $115. I will definitely return them and order from Amazon if I decide that's the route I need to go. Great information.

Still, after further research online, I'm getting the sense that those O2 sensor codes don't necessarily correspond to bad O2 sensors, just that the O2 sensors notice that there is a lean condition and they are trying to compensate for it. I already know this from my 171 and 174 codes. The Internet says to check for vacuum leaks, and all the basics, then move on to O2 sensors. Which I feel like puts me back to square one, and the new codes only gave me information that I already knew, only adding that now the O2 sensors notice it. Thinking about it, that would explain my rough idle - if the O2 sensors are constantly overcompensating for the lean condition, the rpms would fluctuate dramatically, right? But that doesn't lead me to believe my O2 sensors are actually bad.

I've ruled out the EGR and IAC valve so far. The vacuum hoses are near impossible to get to, so I plan on removing the throttle body this weekend and giving them a good inspection. I tried spraying with carb cleaner but it is so hard to listen for a change in idle when the rpms are already fluctuating so much.

tmclem

It is the 5.4L engine, and what would indicate to me that I have a bad PCV? The PCV hose itself and the 90 degree rubber piece seem to be intact. Is there a visual test for the actual PCV that would tell me it's bad? It has a little bit of oil residue in it but I assume that's normal. Thank you for your reply.

Tackle

Pull the pcv out. If should rattle. Cheap to replace, can fix a host of problems.

The hose has an elbow that attaches at the back of the throttle body area. It can develop cracks or leaks. Pull it off and inspect. You'll need to be nimble to get at it.

Here is a good read on your first two codes: http://troubleshootmyvehicle.com/for...d-p0174-page-1

kjburns

I'm not a mechanic and won't pretend to know the answer, but I would refer back to your original post.
In my experience, when a repair leads to another, unrelated repair, it's time to look back at something that happened. It's easy to knock a hose loose and miss it. I've done it and been fortunate to find the culprit without wasting a lot of time. Replacing a serpentine belt and changing the oil shouldn't suddenly cause it to run lean.

Carcrazygts2

Elbow on the back side of the intake for the pcv is probably ripped. Also the P1131/1151 come up when the Oxygen sensor is no longer switching. If they have 200K+ on them They should be replaced. If the PCV eblow on the back of the intake is intact and not ripped try cleaning the MAF with MAF cleaner. Also how long as it been since the vehicle has had a plugs?

tmclem

I pulled the throttle body today, and sure enough, the elbow on the back of the PCV pipe was cracked. Thanks for all your help.

Tackle

Your welcome! You put the new one in? Runs good now?