CEL P0171: Bank 1 Too Lean

[jersey_emt]

I'm throwing this CEL.

From what I've read, here are some possibilities.

1. Leak in intake tract after MAF (checked and triple checked, can't find any leaks
2. Vacuum leak (checked, gauge shows 20 vac)
3. Dirty/Malfunctioning MAF (how to clean/test?)
4. Bad/sticking EGR valve (how to check?)
5. Fuel pump (doubtful, as I can clear the code, turn the car on and the CEL sometimes comes on after a few minutes of idling
6. Bad front O2 sensor

Other symptoms:
1. Occasional drop in RPMs when idling
2. Spark plugs are due for a change soon (29K miles)

Any thoughts?

[jersey_emt]

Car runs perfectly other than idle.

Mods: Injen CAI converted to SRI, Spool hardpipes. Stock boost.

[Dexter]

Hmm my friends speed is doing this with Injen CAI and Apex DP, stock boost.

we also dont know wtf it could be, checked MAF, leaks, and we were gonna swap front O2s but never did.

[BOOSTR]

Never had a CEL, but I too suffered the occasional RPM drop while at idle. Particularily after a long drive. I changed the sparkplugs and it seems to have gone away. I am running an Apex catless and Injen too.

Change your plugs and see what happens.

[Sixmil]

I have the drop in RPMs at idle, sometimes its pretty rough and almost kills the engine and then quickly revs up. Pretty much have had this as far back as I can remember.

-Six



Never had a CEL, but I too suffered the occasional RPM drop while at idle. Particularily after a long drive. I changed the sparkplugs and it seems to have gone away. I am running an Apex catless and Injen too.

Change your plugs and see what happens.

[pdhaudio83]

dont think it could be EGR, i think it'd be the O2....

[pdhaudio83]

and if your spark plugs were bad, you'd be getting misfire codes, so i doubt its the plugs...

[Dexter]

have you tried just resetting the ECU? i think it might have something to do with the injen.

[jersey_emt]

Code comes back after resetting ECU

[Dexter]

Try putting the stock airbox on?

[pdhaudio83]

only thing i can think of is the MAF. theres something happening somewhere that more air is being pulled in than normal or something like that. Otherwise the MAF itself. hmm.

[pdhaudio83]

A code P0171 may mean that one or more of the following has happened:

* The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters (K&N, etc.) can cause the MAF to become dirty if the filter is over-oiled
* There could be a vacuum leak downstream of the MAF sensor.


so the question is, have you cleaned your airfilter lately?
otherwise, you COULD (unlikely) have a clogged fuel filter
also check your PCV valve.

[jersey_emt]

Nope haven't cleaned the filter lately....it's also due for cleaning

[Aaron]

i went to the dealer for this as well last week

all those Dip shits did was reset the PCM. hasn't come back yet.

[BOOSTR]

Forgot to mention, I also changed the PCV valve when I changed the plugs. That combination seemed to solve the erratic idle. But I never had a CEL like you. Get 4 plugs and a PCV and put them in and clear the PCM. I did not alter the CAI set up though. Good luck in getting it resolved.

[akhilleus]

To clean the MAF you can get this air cleaner that is used on electronics and sensitive equipment. Its just a pressurized can of air. that might help.

[^tyrant^]

i have gotten this code many times now, and i have yet to figure out why. i took it to mazda they claim its a bad O2 BUT they didnt replace it. that was the first time mazda looked at it.. I just got my cat back today from mazda agian but this time i had many other problems for them to look at like overboosting to 15 psi, coolant leak etc. ... well the car is still over boosting go figure. well anyway back to the topic they are telling me now that the CEL is from the muffler that i got put on the car, that its leaking. i told them bullshit i brought the car in once before, when i didnt have the muffler and you told me it was a bad O2 but didnt replace it. so im kinda stuck right now with that, im getting a full catback put on then im taking it back and saying the exhaust leak is fixed, not fix the car right this time.

they did replace some parts
By-pass air control valve and/or gasket
boost control assy
air vlv
boost sensor, R&R

and now my idle is better and stable and im not stalling at redlights

[BlkZoomZoom]

What the hell is a boost control ass.?

JerseyEmt- Bring it to the dealer, let them check it out. System too lean codes are nothing to be messed with. Do not try diagnoising a car by asking what fixed other peoples cars, its a bad idea. Also do not just start replacing parts. Diagnoistic procedures are there for a reason, let them use it.

Pay the 1hr. to have the check engine light diag'ed. Then, if its something easy to do, replace the parts the tech. reccomended, if not under warranty.

[^tyrant^]

What the hell is a boost control ass.?


hell if i know, all i know is that didnt fix shit that was wrong, and i forgot to mention that my belt is coming off the pully and they didnt fix that!@!

and my turbo sounds like ass when its spooling so there is something wrong there but they wont replace it, the gasket on the turbo mani is shot and leaking but they say its not! im just going to keep taking it back to them until they fix it correctly

[pdhaudio83]

boost control assembly lol

[kokioki]

Hey Jersey, I got the same exact problem - even the erratic idle, etc.

My mechanic buddy prompted me to use electronic contact cleaner (as did Dexter) on the MAF to clean it.

Now I just have to find me some electronic contact cleaner and a half hour...

[AFaceInTheCrowd]

i get this cel randomly. but i think the reason is because i have a breather instead of the cam case vent hose plugged into my aem intake.

[Aaron]

isn't there a mazdaspeed mechanic on this board somewhere?

[pdhaudio83]

apparently not.

[akhilleus]

Could it be the injectors?

[pdhaudio83]

they could have a clog, but at such low mileage i doubt it

[BlkZoomZoom]

Take it to a dealer.

It is impossible to diagnois cars over the internet.

And yes, I am a Technician.

[Aaron]

Take it to a dealer.

It is impossible to diagnois cars over the internet.

And yes, I am a Technician.
That is the problem at least my dealer didn't do shit. they just reset the ecu and did nothing.

[BlkZoomZoom]

Depending on the situation I may also "not do shit". If no problem can be found, and all systems are working properly, no shit can be done. Has the code come back? If not maybe "not doing shit" fixed the problem it didn't have.

[1338]

hell if i know, all i know is that didnt fix shit that was wrong, and i forgot to mention that my belt is coming off the pully and they didnt fix that!@!

and my turbo sounds like ass when its spooling so there is something wrong there but they wont replace it, the gasket on the turbo mani is shot and leaking but they say its not! im just going to keep taking it back to them until they fix it correctly this problem with his car had be going go for quite some time now! we went out to eat tonight and i heard the turbo, it does not sound good AT ALL!
RICK CASE MAZDA = DUMBASSES for letting that car out of the shop.

[cosmo420]

i am having the same problem here and my scanner is telling me there is a low voltage reading so i replaced my custom mil with a new resister and a week later it came on again for the same exact reason, i am tempted to just remove the resister i put in and go with the double non fouler trick for the o2 to see if it does it again, and when my light comes on the car runs like ass and i am getting anywhere from 240-250 on a full tank of gas compared to 330 in the past which pisses me off

[kokioki]

Yeah Cosmo, I'm getting about as good mileage as an H2 or Escalade or something... running pig rich.

Let us know if the double non fouler trick works, I'd be interested to try it.

[kokioki]

Take it to a dealer.

It is impossible to diagnois cars over the internet.

And yes, I am a Technician.

While I agree that it is impossible to diagnose a car on the internet, taking it to the dealer may not always be an option. I am experiencing exactly the same problem with my speed, so chances are if Jersey finds a solution, I'll be able to recreate his results with his same actions.

Some of us may also have voided our warranties ;)

[cosmo420]

i will try by later this evening kokioki,and let you know, im too lazy to un bolt my mods and take it in from my experience at dealerships with my LT-1 has made me avoid the dealerships entirely

[jersey_emt]

Cleaned the air filter and MAF, and cleared the code. Hasn't come back in a day and a half yet.

I still have my warranty, the only problem is that my dealer will only give a loaner vehicle to those over 25. And I'm only 23.

[Ryoga28]

If you still have warranty couldn't they just get you a rental instead of a loaner (enterprise)?

[Aaron03MSP]

i had that exact same problem when i bought my car. i took it to the dealer 3 times or so, they changed the o2 didnt fix problem. changed computer or something, didnt fix, then they said it was a small hole in a nipple hose that attaches to the bpv or somthing. so far i havent seen that cel(knock on wood)

[kl_03maz]

sorry to dig up old threads but I'm experiencing a similar problem...
Its not throwing a code, which is pissing me off, however there is hesitation.

I have posted this in another thread already that I created, but I found this info that sort of seems like what I'm experiencing.

I'm experiencing a fast rpm drop that feels like the engine is either not getting enough fuel, bad spark, or not enough oxygen. It drops from about 700rpm to about 2-3rpm and then comes right back. This happens at Idle, when in Drive at a stop, when in neutral, when in park and when in reverse. I also experiencing... not an rpm drop but hesitation when steping on the gas from a complete stop. I do not experience this at all when at speed or stepping on the gas when at speed, only from a stop.

Needless to say, this is getting rather annoying. As I said.. no code is thrown, so I sort of feel like I'm looking for a needle in a hay stack. I did experience my was turning over yesterday and it took longer to grab then usual. I'm hearing a whine from my alternator around 2500rpm.

I kind of don't want to take it to the dealership to tell me they can't find anything wrong, there's already a mechanic at my work that thinks I'm making this up.

Things I can think of:
Fuel Pump (no code would be thrown that would pinpoint the fuel pump, would say something like.. cylinder 2 misfire or some stuff, or tell me the regulator lost pressure, but not pointing the fuel pump directly, from what I understand anyhow...)

PCV - As mentioned in this thread

Alternator

Spark Plugs (But the plugs look good and there is no misfire code)

Spark Plug Wires (I jiggle them and there no drop in rpm due to a misfire or anything)

Plugged up injectors - as mentioned in this thread

Plugged up Cat - creating too much backpressure? (might explain that it happens when stepping on the gas, but when at speed the exaust flow is higher, forcing exhaust through the plugged section, though I haven't really noticed a performance drop.)

*proceeds to rip out his hair*

Cheers

[BlazinYellow]

I have all the same problems as stated on the board. I had a perrin short ram intake on my car and I put the fac. intake back on and replaced the MAF and reseted the comp. The CEL came back after 4 days. Ihave talked to other mechanics and one guy told me that my pre cat is clogged or somthing of that nature or a bad O2 sensor. I also replaced all the lines from turbo to my recuirculating valve and the one to my intake and the vent case hose. The were all in bad shape. Still have the CEL. I am goin to cut my pre cat off in a few days and put a pipe up there. Hopefully that works.

Also I my turbo is making a funny noise also when it spools up, but it can be heard better when I get on it and push the clutch in to stop. It doesn't sound good though. Has anyone had any fixes on these problems yet?

[kl_03maz]

Just to update you all....

A couple months ago, (I know.. late update) My car FINALLY threw a CEL while on my lunch break, on my way to the dealership to get a new spark plug wire cuz I was convinced that I was having a misfire.

Well... I got the thing scanned and both Coil Packs replaced for $113.00 under warranty.

It appeard to be a Cylinder 2 Misfire, so they replaced both Coils.

:)

No Problem since... except well... for my alternator taking the cake on me.

[BlazinYellow]

has anyone had the problem with the PO171 code fixed?

[speedcicle]

Yea i had that code a long time ago so i use the corksport exhaust with the spark plug non foulers for the 02 sensor, and the split second afc from dsmconvert. I have had no lean condition or check engine light in over a year and a half.

[overboost03]

I'm throwing this CEL.

From what I've read, here are some possibilities.

1. Leak in intake tract after MAF (checked and triple checked, can't find any leaks
2. Vacuum leak (checked, gauge shows 20 vac)
3. Dirty/Malfunctioning MAF (how to clean/test?)
4. Bad/sticking EGR valve (how to check?)
5. Fuel pump (doubtful, as I can clear the code, turn the car on and the CEL sometimes comes on after a few minutes of idling
6. Bad front O2 sensor

Other symptoms:
1. Occasional drop in RPMs when idling
2. Spark plugs are due for a change soon (29K miles)

Any thoughts?
If you have a air/fuel meter watch it. does the meter switch lean to rich or does it hang in the lean for awhile? My car does the same thing and mine apears to have a lazy upstream 02 sensor.

[Delivery_Guy]

I've been getting this same code off and on for a little while now. The dealership wants to replace the wastegate actuator...but that will be my third one in 75,000 miles. The first two they replaced the entire turbo under warranty for stuck wastegates. I spent a bit of time replacing vacuum lines and putting clamps on my boost gauge lines and the cel went off on its own right after that and hasn't been back in about a week. My dipping idle has also been better, though I really think one week is too soon to say it's fixed.

[levison]

i now have the same CEL. my wastegate actuater went a couple days befor the code so i hope my new one will get rid of the CEL.