P0171 - System Too Lean

[jdoggsc]

Hey all, I just bought my first mazda (2003 protege). It has a CEL on and my reader says P0171 - Lean Mixture. The funny things is that a week before, I test drove another mazda protege on a used dealer lot and it came up with the same error.

Since i've only driven 2 mazda proteges and they both have the same error, it seems like this is a common problem? or else it's just a coincidence?

I know what a lean mixture means, but I'm just wondering what people do to fix this. I searched a bit, and didn't find a lot of useful input. Here's where I am at this point.

I reset CEL to see if it was a stale code. it just stayed pending for an entire 200-mile trip, then the code and light came back after a little city-driving. I tried spraying some starter fluid around the MAF, the throttle body, the intake manifold, and the vacuum hoses and the revs didn't pick up, so I don't think it's a vacuum leak. Are the MAF sensors known to by flaky on these cars? I'd rather not buy a new one, but has anyone rectified this by buying a new O2 sensor?

The PO said the light would turn off and on for years and he just put some injector cleaner i've never heard of (it's in a box in the trunk) in the gas and hoped that would clean it out.

a little more info, in case anyone has encountered this: it seems to do fine in accelerating and driving at constant speed, but at idle it will be fine for several seconds and then occasionally shudder (the rpms will momentarily drop to 500 or below) and then i'll get a pending P0171 error code.


what is you experience with this? any ideas on things i can do to troubleshoot?

 

[vw.fe2o3]

What seems to be quite common lately due to the age of these cars is the large hard rubber air intake tube running between the air box and manifold is old and cracking. This causes a vacuum leak and trips this cel.
Pull yours off and take a close look all around and underneath. Mine just went a few months ago as well and had the same code.
Auto parts shops readily carry these under $60

 

[jdoggsc]

thanks for the reply and suggestion.

i've got an [aluminum] cold air intake, so luckily I don't have to worry about the decaying rubber there. I sprayed starter fluid (for my motorcycle) all over it and the manifold and vacuum hoses around the manifold and the RPMs never picked up. I'm pretty sure there's no air leak.

 

[vw.fe2o3]

In that case, you might want to clean the MAF using a can of MAF sensor cleaner in the spray can... $5-$6 from most any parts store. I've heard you should spray only, don't touch/handle it.
That's about the only other thing it should be... dirty or bad MAF. Hopefully just dirty If it comes to replacing it, Rockauto sometimes has pretty good prices if you aren't in a huge hurry for something.

 

[jdoggsc]

i'm pretty sure i found the problem.

it's on the back side of the CAI near where it meets up with the throttle body. I could never have seen it if i didn't remove it. It looks like it was cut out with a tool by a previous owner (don't ask me why). I closed it off with several tightly-wound layers of tape and I think it's fixed now. I drove it around for about 5 miles and my long term fuel trim went from about 10% to around 0%, and the idle stabilized again. I want to drive it around a bit more to make sure, but i can't imagine it wouldn't fix it.

p.s. i have no idea why the revs would not have increased when i sprayed around it with brake cleaner and instant start. i was sure because of that that I didn't have any leaks in the piping. oh well.

 

[IshSonP5]

i'm pretty sure i found the problem.

it's on the back side of the CAI near where it meets up with the throttle body. I could never have seen it if i didn't remove it. It looks like it was cut out with a tool by a previous owner (don't ask me why). I closed it off with several tightly-wound layers of tape and I think it's fixed now. I drove it around for about 5 miles and my long term fuel trim went from about 10% to around 0%, and the idle stabilized again. I want to drive it around a bit more to make sure, but i can't imagine it wouldn't fix it.

p.s. i have no idea why the revs would not have increased when i sprayed around it with brake cleaner and instant start. i was sure because of that that I didn't have any leaks in the piping. oh well.

How the heck did that happen?!?!

 

[jdoggsc]

How the heck did that happen?!?!

I looked around for anything it would have been rubbing against that might have done that (especially since getting a big chunk of Aluminum in the intake should have been catostrophic) but it looks like it was cut out with a dremel or the like. Why? beats me. i'm the 3rd owner of this car and the original owner liked to mod it. Konig rims (not bad, actually), an amp in the trunk, a better stereo (although be put the factory one back in afterward, with a few missing garnishes), NEON LIGHTS under the front and rear bumpers that were integrated with the stereo, a car bra, and a couple other things that i know are there but aren't coming to mind just now. most of the engine mounts were completely torn, so he liked to hot-rod it too.

This is my best guess. The lean condition would make the ECU compensate for it by putting too much fuel in (hence the 10% Long-term fuel trim) and inducing a rich condition. The result is more explosion and more power (since the normal map trys to maintain the mixture just slightly lean for economy). Admittedly, the car doesn't pull as hard as before. It was hard not to squeal the tires from a stop, but now it's more tame. The effect, as well as I can surmise, is the same as "chipping" your car to get more power out of it--just cheaper.

 

[2003.5_MSP]

I that was the pipe by your throttle body then that looks like to me it was rubbin on the master cylinder reservoir

 

[jdoggsc]

there's no damage to the master cylinder. it was ground out with a tool.

 

[jdoggsc]

I that was the pipe by your throttle body then that looks like to me it was rubbin on the master cylinder reservoir

correction to my previous comment. It was definitely rubbed open by the master cylinder. I guess I didn't take a good look at it when I put it back in, except that the code came back because the master cylinder wore away my band-aid fix. Idiot move on the PO's part to put in a CAI that didn't fit without any interference.

 

[HawaiiP5]

[Entering this into the thread to show how common the problem is]

Had the same problem with my Protg 5 a few months ago.
Code: P0171 Bank one too lean

Changed O2 sensor again (which I had done approx. 6 mos. prior)...no joy (same code exists and trips again)

Started checking vacuum leaks because the engine was throttling weird when the engine "shook" more / engine almost stalls in low idle. While checking for vacuum line leaks...bumped that hard rubber hose and noticed a huge gaping crack in it. Shook the hose again...engine dies...bam, problem located. Changed out the hard rubber hose with a new one for $60 from O'reillys...problem solved...code erased itself. Engine runs great again!