Very lean code idling at 900RPM no other drivability issues

[Sagarin12]

I have a 2005 Trailblazer w/ 4.2 I6... MIL came on with a P0171 system too lean bank 1 code. Also had 2 pending codes: P0131 O2 sensor circuit low and P1133 heated O2 sensor insufficient switching bank 1 sensor 1.

I have had a gurgling noise coming out of the air intake, have worked my way down to determining the secondary air diverter valve is stuck open, and the gurgling noise is exhaust being pushed backwards through AIR pump and up into the intake... Plan on putting a new diverter valve on this weekend.

I pulled PIDs at IDLE (900rpm) and in PARK after driving for half hour..
FUELSYS1----OL FAULT
LOAD_PCT(%)----- 39.2
ECT (F)----------179
SHRTFT(%)------0.0
LONGFT(%)------21.9
MAP (PSI)-------5.4
RPM--------------903
SPARKADV-------14.5
IAT(F)------------55
TP%--------------17.6
AIR_STAT--------OFF
O2B1S1(V)------0.005
O2B1S2(V)------0.970


Do any of those seem unusual? I also had scanner hooked up as I was driving, and noticed that at the slightest touch of the gas pedal the LOAD_PCT pid would jump way up. At idle and in gear like at a light, the LOAD_PCT hovered between 40 and 45.
I disconnected the tube from the diverter valve to the pump at the pump and had exhaust coming out.

Any help is much appreciated.

 

[The_Roadie]

First time I've head of that failure mode!

Long term fuel trim is hosed. Get rid of the exhaust coming into the intake by any means possible.

You didn't share your mileage, but if it's over 100K, it's time for new plugs and an O2 sensor. Use only Delco 41-103 plugs and the AC Delco sensor.

Welcome!

 

[IllogicTC]

I have a 2005 Trailblazer w/ 4.2 I6... MIL came on with a P0171 system too lean bank 1 code. Also had 2 pending codes: P0131 O2 sensor circuit low and P1133 heated O2 sensor insufficient switching bank 1 sensor 1.

I have had a gurgling noise coming out of the air intake, have worked my way down to determining the secondary air diverter valve is stuck open, and the gurgling noise is exhaust being pushed backwards through AIR pump and up into the intake... Plan on putting a new diverter valve on this weekend.

I pulled PIDs at IDLE (900rpm) and in PARK after driving for half hour..
FUELSYS1----OL FAULT
LOAD_PCT(%)----- 39.2
ECT (F)----------179
SHRTFT(%)------0.0
LONGFT(%)------21.9
MAP (PSI)-------5.4
RPM--------------903
SPARKADV-------14.5
IAT(F)------------55
TP%--------------17.6
AIR_STAT--------OFF
O2B1S1(V)------0.005
O2B1S2(V)------0.970


Do any of those seem unusual? I also had scanner hooked up as I was driving, and noticed that at the slightest touch of the gas pedal the LOAD_PCT pid would jump way up. At idle and in gear like at a light, the LOAD_PCT hovered between 40 and 45.
I disconnected the tube from the diverter valve to the pump at the pump and had exhaust coming out.

Any help is much appreciated.

Welcome to the site! You've come to the right place. Here's an obligatory link (not related to your current issue, just a backstory on the site) http://gmtnation.com/f5/welcome-gmtnation-com-heres-story-226/

Yes, this does look strange.
1.) The O2 sensor stay that low, consistently? It's supposed to be fluctuating between about 0.1 and 0.9. This may be caused by excess unmetered air throwing off the reading pretty far.
2.) MAP seems kinda low. My MAP usually sits at maybe 9.x at idle. This could be pointing you in the right direction.
3.) LTFT >20. It shouldn't ever be double-digits unless something is wrong. STFT may dip a little into the double-digit range here and there but shouldn't sit there either (I see it's not at this moment).
4.) High idle. The PCM may be doing this as part of its anti-stall system, it should be around 625. (And yes I have about 9 on my MAP at this speed)

When underhood with the engine running, do you hear any hissing from the area of the air intake assembly? A loose vacuum line could mess with this, there are 3 lines. One on the bottom of the resonator plugging into the top of the block (you can peek under the plastic thing that reads VORTEC [that's your resonator] on the front side to see if it's okay. May require removal of the resonator which is a trivial job for further inspection.) There is also a line running to your brake booster, and a line that should be capped on the intake manifold. The intake manifold itself is that oval black plastic piece on the driver's side. Toward the front of the intake there'll be a long prong poking out pointing toward the resonator, this should have a rubber cap on it from the factory.

If you don't hear hissing, I'd point directly to the intake manifold bolts. They have a tendency to work their way loose over time. Take a look through this thread: http://gmtnation.com/f25/im-bolts-8096/ also search intake manifold bolts and search through the forums, there's plenty of other threads on the exact same issue. The bolts need to be torqued to 12 lb-ft (144 lb-in). So yes, you'll need a torque wrench!

The p0171 will stay gone if one of these things shows an issue and is repaired, and the other ones may stay away too. If not, you may have a flaky O2 sensor also.

 

[Sagarin12]

First time I've head of that failure mode!

Long term fuel trim is hosed. Get rid of the exhaust coming into the intake by any means possible.

You didn't share your mileage, but if it's over 100K, it's time for new plugs and an O2 sensor. Use only Delco 41-103 plugs and the AC Delco sensor.

Welcome!

Truck has 180K on it. Replaced plugs when I bought it about 6 months ago.

I couldn't find anything on this problem either... When I was writing the PIDS down the short term fuel trim was at 0.0, but it's usually up around +17% with the long term where it was in the original post.

Do you think the exhaust going backwards through the AIR system could be causing the high idle? I wouldn't think exhaust backpressure would be enough to raise the idle 300rpm.

 

[IllogicTC]

Truck has 180K on it. Replaced plugs when I bought it about 6 months ago.

I couldn't find anything on this problem either... When I was writing the PIDS down the short term fuel trim was at 0.0, but it's usually up around +17% with the long term where it was in the original post.

Do you think the exhaust going backwards through the AIR system could be causing the high idle? I wouldn't think exhaust backpressure would be enough to raise the idle 300rpm.

That and it should trigger P0411 and/or P2432 (there's another thread on these very codes I'm trying to figure out, and research of these codes tells me the system is able to see that happening)

I'm still curious on the intake manifold bolts. Very common issue, and very likely to give these symptoms.

 

[AtlWrk]

Do you think the exhaust going backwards through the AIR system could be causing the high idle? I wouldn't think exhaust backpressure would be enough to raise the idle 300rpm.

To clarify #4 from IllogicTC's first post: the idle speed is 100% computer controlled and should normally be around 625 or so. When the computer detects a problem or poor idle quality it will intentionally raise the idle RPM to 900 rpm to keep the engine from stalling. It's not that your problem is directly causing the increase in idle by changing the airflow or some similar mechanism--it is simply the computer's response to a detected problem.

Excess oxygen in the exhaust stream from a gross leak will flatline your O2 sensors and put your LTFT through the roof. I imagine most of your issues will clear up when you replace your check valve.
I agree with checking the intake manifold bolts too--I've added it as part of annual maintenance. May or may not be contributing to your issue but I'd put money on some of them being loose.

EDIT: Another thought: there's a thread floating around here about disassembling, cleaning and manually cycling the check valve with a pair of vise grips to get it unstuck. May be worth a shot and save you some serious coin on a new valve.

 

[Sagarin12]

To clarify #4 from IllogicTC's first post: the idle speed is 100% computer controlled and should normally be around 625 or so. When the computer detects a problem or poor idle quality it will intentionally raise the idle RPM to 900 rpm to keep the engine from stalling. It's not that your problem is directly causing the increase in idle by changing the airflow or some similar mechanism--it is simply the computer's response to a detected problem.
EDIT: Another thought: there's a thread floating around here about disassembling, cleaning and manually cycling the check valve with a pair of vise grips to get it unstuck. May be worth a shot and save you some serious coin on a new valve.

I could try that, but I'm lucky, work at a SMALL parts store and can get it for just above our cost (boss rounds up to next $10 bill, or adds $5 whichever is more). Hopefully replacing it tonight during/after my HVAC class. Heated shop, and all the tools I could want.

 

[Sagarin12]

Installed new valve today. Poured some water in the old one, and it just poured right back out. Valve was in fact stuck open.
Cleared codes after installing. When I cleared the codes, idle dropped to normal 600-650 range but was slightly rough at first, eventually smoothed out. went for a ride around the block, idle bumped back up to 900 RPM, and the bank 1 lean code was back. Going to try with just the valve for the weekend. See if it's just taking time for computer to lower LTFT.

 

[AtlWrk]

Can you see live data for your O2 sensors? Does the upstream sensor values move at all?

I would speculate that .005V (O2S1B1) is not an actual reading of excess oxygen but rather just a dead or disconnected sensor. Replacing this would be the next step and as Roadie mentioned only use AC Delco.

At least you know the valve needed to replaced regardless. Nothing lost

 

[Sagarin12]

Can you see live data for your O2 sensors? Does the upstream sensor values move at all?

I would speculate that .005V (O2S1B1) is not an actual reading of excess oxygen but rather just a dead or disconnected sensor. Replacing this would be the next step and as Roadie mentioned only use AC Delco.

At least you know the valve needed to replaced regardless. Nothing lost

I just have a cheap little $60 scan tool (was honestly surprised it even had live data PIDS for that cheap), but the O2 sensor voltage is changing. When I hit gas while in park voltage dropped to about 0.290V, at idle (800RPM cold engine) it hovers around 0.410-0.425V

 

[The_Roadie]

Only the downstream (post-cat) sensor should be steady, proving the cat is doing its job.

The upstream (exhaust manifold pre-cat) sensor should wiggle from around 0.1 to 0.9V once or twice per second. Anything steady low or high or slowly wiggling is bad.

 

[IllogicTC]

Only the downstream (post-cat) sensor should be steady, proving the cat is doing its job.

The upstream (exhaust manifold pre-cat) sensor should wiggle from around 0.1 to 0.9V once or twice per second. Anything steady low or high or slowly wiggling is bad.

Also, downstream should read in around the .7-.8 volt range. If downstream is giving a solid number but it's low, could mean excess oxygen entering somewhere in the exhaust (cracked manifold, etc.).

 

[Sagarin12]

Only the downstream (post-cat) sensor should be steady, proving the cat is doing its job.

The upstream (exhaust manifold pre-cat) sensor should wiggle from around 0.1 to 0.9V once or twice per second. Anything steady low or high or slowly wiggling is bad.

Upstream O2 sensor is dead as a dodo bird. Kept scanner hooked up all the way home, never budged from 5mV.

 

[IllogicTC]

Upstream O2 sensor is dead as a dodo bird. Kept scanner hooked up all the way home, never budged from 5mV.

That'd do it

Low voltage means a lot of oxygen in the exhaust (under normal operation), which is compensated with a +fuel trim. That's why yours is through the roof.

Then the voltage goes high (low oxygen), which is compensated with -fuel trim.

Time to get yourself a new sensor and a sensor socket if you don't have one already. Look around on here for posts about people replacing it, there should be part numbers, socket sizes, tips and tricks for freeing it from the manifold.

 

[Sagarin12]

That'd do it

Low voltage means a lot of oxygen in the exhaust (under normal operation), which is compensated with a +fuel trim. That's why yours is through the roof.

Then the voltage goes high (low oxygen), which is compensated with -fuel trim.

Time to get yourself a new sensor and a sensor socket if you don't have one already. Look around on here for posts about people replacing it, there should be part numbers, socket sizes, tips and tricks for freeing it from the manifold.

I have an O2 sensor socket. Question is WHERE... Oh well, if I can't find it I'll borrow the neighbor's
As for getting it out, I usually just soak the socket down in penetrating oil, then drive around, let manifold heat up, more penetrating oil, then hope for the best. I know NOT to get Bosch sensors, has anybody had/heard of experience with Denso sensors? That's the only brand my warehouse stocks. They can get AC Delco, but it's a special order part.

 

[IllogicTC]

I have an O2 sensor socket. Question is WHERE... Oh well, if I can't find it I'll borrow the neighbor's
As for getting it out, I usually just soak the socket down in penetrating oil, then drive around, let manifold heat up, more penetrating oil, then hope for the best. I know NOT to get Bosch sensors, has anybody had/heard of experience with Denso sensors? That's the only brand my warehouse stocks. They can get AC Delco, but it's a special order part.

This motor seems to sniff out anything non-OEM on "critical" components. I would heartily suggest going with AC Delco.

GM 12586996
AC Delco #213-1698

I think someone around here tried Denso or Bosch or something but I can't remember how it ended up turning out. Someone may have an answer to your question.

 

[BRomanJr]

I have an O2 sensor socket. Question is WHERE... Oh well, if I can't find it I'll borrow the neighbor's
As for getting it out, I usually just soak the socket down in penetrating oil, then drive around, let manifold heat up, more penetrating oil, then hope for the best. I know NOT to get Bosch sensors, has anybody had/heard of experience with Denso sensors? That's the only brand my warehouse stocks. They can get AC Delco, but it's a special order part.

IIRC, Denso is one of the manufacturers for AC Delco O2 sensors, maybe not all parts though. I have used Denso O2 Sensors (and many other Denso branded parts) on my Envoy and several other GM vehicles and no problems. Always had issues with Bosch.

You can't go wrong with AC Delco.