Mixture too lean, P0171, P0174, P0313

[325cijohnny]

I'm having the same problem my 325ci is throwing too lean codes according to the shop all the vac lines have been repaired, maf sensor wad replaced, cam and crank sensors have been replaced and plugs have been changed I have a fuel filter on the way just clueless on what is causing the problem car runs ok just every now and then when I put it in drive or reverse its jumpy or just completely cuts off no clue what it could be all I get are the too lean codes

[danewilson77]

Did they replace the upper and lower intake boots? You made no mention of this.

I would however hope, the shop did this first.

[325cijohnny]

They didnt replace them i know some of the boot was torn and was told and shown that he sealed it off with tape and put some sealer on it and said there were some lines they replaced and the car ran 100 percent better then it did just still throws the codes and here and there cuts out when i put it in gear. Ill give the car gas and theres a delayed response and then car kinda jumps and cuts off

[danewilson77]

Oh boy. I think you should use a different mechanic. You most likely need a new lower intake boot, if not an upper as well.

You may have more than one thing going on here as well.

I say REPLACE the boots, clear and check codes, then lets go from there.

[bwh3200]

How are you guys getting the hose clamps off? Mine are upside down!

[danewilson77]

I used an offset, very small box end wrench. I have a pic somewhere.

The other beneficial tool for this is a flex driver...and small socket.

What I usually do...is buy 2 new boots...upper and lower, and I just cut the lower off, whick frees up the room. I always take the DISA out, which also helps a smidge....

[nathancarter]

The first time I did it on my (sold) 325i, to remove the hose clamps I used a flexible screwdriver and a large assortment of swear words.

The second time I did it on my (current) 330i, like Dane said I just cut off the old parts with a razor, to make room to access the hose clamp. I think I removed the ICV with the last part of the small hose still attached, then removed the hose clamp from the ICV once it was out of the car. Then when it goes back together, put the hose clamps on in any direction that gives you easy access. Pointing straight up worked for me.

[joegha1]

i have a 2002 525I E39 which due for emision testing at the end of January.
I have the error code P0444 and the p0171, P0174 previously have read about the intek boot and checked it, mine looks very good. i had error code p0102 not sure but it was about mass air sensor. later which was the mass air flow sensor, and ordered one and replaced it and cleard the code as was the only code took the car for emission control test, and was rejected as oxygen sensor not ready, was only 2 days after i cleared the code.. so waited for another 5 days and 3 codes popped up the p0444, p0171,p0174.

here is my plan after reading all these posts.
1. to replace the fuel cap..
2. i have the new boot ordered and planing on replacing it

if the codes are still there or re appear after a week of driving?

I am thinking about replacing the purge valve or the breather valve.
Is this a good plan or what?

any inputs or suggestions will be appriciated
Joe

A little update Changed the fuel cap and filled the car with premium grade gas. And the error code has gone. Put my error code reader and checked to see if any errors saved? Well all the 3 codes are still saved in it.

Plan. To run for few days and check if the saved codes are removed or I have to do the erase myself?
Hope it clears by itself.

[drmoreau]

good luck, thousands of dollars and I was never able to eliminate this problem. well I got the codes to stay gone, but my idle was still off.

[xmntx]

After putting the obd-2 scan and checking the MAF its running at 3.90 mg at idle with engine running is that normal??or is it too low and the revs smtimes do fall very slightly. Want to see if its the MAF gone ...

[drmoreau]

good luck with this one guys. i sold the car and it still wasn't fixed...

[joegha1]

Ok here we go again in three weeks
Week one Had only error p0171
Week two Had error p0174 only Also week three
Today I checked I have both errors p0171 and p0174
Emission is due the end of this month and planing on taking and checking every vacuums tube / hose And check the CCTV which I red many people found that to be the problems . I have ordered the fuel filter and also going to replace it. This weekend is the mother of all weekends and going ti fix it or break it,
Well
I need all the luck on this one , the car runs fine but this error code has to go
Joe

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[jwisener]

Are you guys able to do all this boot and hose replacement from the top or do you have to put the car on ramps and work from below?

Thanks,
jw

With your engine running, try to slowly and slighty remove your oil cap. There should be a slight vac, but if it's a very strong vac. and the engine stumbles hard when you remove it then it probally needs a "Crank case vent valve." Other places to look for air leaks is the air boot that "Ys" off at the throttle body and Idle control valve (follow your MAF back to your Intake and you will see it). The small hose on the boot that goes to the Idle control valve cracks on some older cars and allows "false air" in, causing your lean mixture faults.

If none of these give you anything, look at your MAF signal as the engine is running (operating temperature WITH THE A/C OFF). IF the MAF reads something other than 11-13 kg (I think it's KG) then you probally have a faulty MAF.

Are you guys able to do all this boot and hose replacement from the top or do you have to put the car on ramps and work from below?

Thanks,
jw

[danewilson77]

From the top. Flex drive extension and offset box end wrench are a must. Also... Buy new boots before you start. Cut the old ones off. It will help immensely.

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[jwisener]

From the top. Flex drive extension and offset box end wrench are a must. Also... But new boots before you start. Cut the old ones off. It will help immensely.

Sent from my Thunderbolt using BF.com

Hey, thanks for the response!

[danewilson77]

But = buy, above.....sorry

[jwd027]

Hey guys i have a similar thing but can see Nathancarter pic of the boot! Can you put it back up? Did you have to take the manifold off to get to this elbow? The pipes are pretty enclosed!

[04bmw330ci]

I had the P0171/P0174 problem on my 04 330Ci. The light would randomly come on - sometimes after a few days, sometimes after a few weeks. I've seen recommendations here ranging anywhere from replacing the O2 sensors to tightening the oil/gas cap and cleaning the MAF.

Before you do any component replacement or risk damaging the MAF, check the MAF boot that goes into the engine block. Press your finger into the boot, especially on the back side where it curves. When I did that my finger went inside the boot through a crack that was not visible from the front of the car.

New boot = ~$20
Time = ~2hrs, mostly because it takes so long to screw the bracket on the engine side once the new boot is on. If you have a flexible screw driver you won't kill your back like I did.

Issues resolved once the boot was replaced:

- Gas mileage went from 24MPG freeway to 29MPG.
- Power became smooth throughout the RPM range. Before this I had no power until I got over 3000RPM.
- Haven't seen the check engine light come on for over 6 months now

If you're interested in the technical details of why this tear throws a lean mixture code continue reading.

The MAF sensor determines the amount of air entering the engine. The ECU uses this data to calculate how much fuel to supply in order to maintain the optimal fuel/air ratio. However, since the boot is torn AFTER the MAF sensor, extra air enters the engine through that tear and goes undetected. This extra amount is not taken into account by the ECU when it calculates how much fuel to provide. Therefore, it results in a lean mixture (too much air). The ECU will normally compensate for a lean mixture by adding extra fuel, but only up to a certain percentage above what it normally supplies. Once that percentage is exceeded and the mixture is still lean, the ECU determines that there is a component failure and throws the error codes that you read out of the OBD II. Since the ECU always provides the maximum fuel amount during lean operation, the gas mileage drops.

Hope this helps.

-Nick

[ch40t1c]

Thanks for the post Nick.

[GreaseJunkie]

I didn't read through this whole thread before I did this, but I ended up cutting the boot off at the manifold to get to the clamp. This was THE BIGGEST PITA JOB EVER! I put a new rack in my old 320i, by myself, on ramps, no lift, and this still takes the cake. There is no good way to put the hose clamps back on, but reverse seems a little better. Definitely use some 7mm angled wrenches, if you have them.

[jon1973]

I've got the Service Engine Soon light on in my 2001 325i, 58k miles. I had it for a checkup at the dealership recently, and they performed some other work under my 2000mile used-car warranty (ECU said the thermostat was sticking open; said warranty has since expired). They gave me a printout of the DTCs, and the other prevalent codes besides the thermostat were P0171 and P0174 with an occasional P0313, plus one that indicated low voltage across the MAF (can't remember the code number). The service advisor suggested that they reset the codes and see if they come back after the thermostat replacement, since the warranty didn't cover the MAF. The light has since come back on and my scan tool says it's the same codes: P0171, P0174, P0313. Fuel mixture too lean, causing an occasional misfire.

Yesterday, I gently cleaned the MAF using electrical contact cleaner (it didn't look dirty, but I cleaned it anyway with three cycles of spraying it then letting it dry). I then cleared the codes and took it for a test drive and the codes didn't come back. I checked it again this morning after driving to work and P0171 and P0174 are pending; I expect the light will come on when I drive it home.

Possibly relevant: there's a high-pitched whistling noise at a certain throttle position. It sounds somewhat like a turbo whistle, and is independent of engine or car speed, dependent only on throttle pedal position. The dealer service advisor said he didn't hear anything unusual.

Any suggestions before I drop a couple hundred on a new MAF?

Thanks.

Try this, on the intake hose remove the MAF sensor then block the hose with a rubber glove. Next if u have an air compressor available remove the small hose connector on the top of the intake hose and hook up the the air line and let a small burst of air in the intake hose hose then listem for any hissing sound comming from the engine. i u do try to locate where its coming from. Worked on two bmw's for me. best way to find an air leak. mines was missing a valve cover nut where air was escaping and crack on the cover also air escaping. code P0171 p0170 .No more codes.

I'm having the same problem my 325ci is throwing too lean codes according to the shop all the vac lines have been repaired, maf sensor wad replaced, cam and crank sensors have been replaced and plugs have been changed I have a fuel filter on the way just clueless on what is causing the problem car runs ok just every now and then when I put it in drive or reverse its jumpy or just completely cuts off no clue what it could be all I get are the too lean codes

Try this, on the intake hose remove the MAF sensor then block the hose with a rubber glove. Next if u have an air compressor available remove the small hose connector on the top of the intake hose and hook up the the air line and let a small burst of air in the intake hose hose then listem for any hissing sound comming from the engine. i u do try to locate where its coming from. Worked on two bmw's for me. best way to find an air leak. mines was missing a valve cover nut where air was escaping and crack on the cover also air escaping. code P0171 p0170 .No more codes.

[nathancarter]

Try this, on the intake hose remove the MAF sensor then block the hose with a rubber glove. Next if u have an air compressor available remove the small hose connector on the top of the intake hose and hook up the the air line and let a small burst of air in the intake hose hose then listem for any hissing sound comming from the engine. i u do try to locate where its coming from. Worked on two bmw's for me. best way to find an air leak. mines was missing a valve cover nut where air was escaping and crack on the cover also air escaping. code P0171 p0170 .No more codes.

This is a pretty good simple test - instead of a smoke test, an air pressure test.

[EXTREMOUSA]

Found it!
As suggested, the intake boot was decayed and torn open on the elbow leading into the idle control valve. The other boot (immediately after the MAF) is also in mediocre condition, so I think I'll replace them both. In the meantime, I've applied my ghetto fix of closing up the hole with packing tape (couldn't find the duct tape). The whistling noise is practically gone and I've driven about 100 miles without any new fault codes.

The hardest part of the job, by far, is that the last two hose clamps were installed (in my opinion) upside down, so they were VERY difficult to access and loosen. When I replaced them I put them right-side-up so I can get to them again when the replacement parts arrive.

Thanks for everyone's advice! I'll post some photos as soon as I have enough posts, and maybe write a quick DIY.

Replacing Intake Boots, Cleaning Throttle Body, ICV


Check it this video .

[ame]http://www.youtube.com/watch?v=o-7keth6soE&feature=player_embedded[/ame]

[nawang]

what is MAF?

[kimmer]

First photo is the location of the failure, with some other parts (Intake, throttle body) moved out of the way. The red arrow is the boot where the hole is. The yellow arrow is one of the two hose clamps that were the hardest part of the job. If you look closely, you may be able to notice that the head of the screw on the hose clamp is not visible - because it's pointing downwards! When I put it back together I reversed the hose clamps so the screw is pointing up.

Second photo is the big-ass hole in the intake boot.

Third photo is my ghetto repair job (yes, I've already ordered replacement parts)

hi I'm the some problem but the whistling noise stops when the engine is warm any idea thanks. kimmer

hello there