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Discussion Starter · #1 ·
Ok so I have been having this problem since I bought the car. It's intermittent, i randomly get the P0174 and I believe 0171 lean mixture both banks along with missfire on low fuel. It's only when the car is driven for a few miles at low rpm. However if I drive the car spirited the cel goes away. I believe I can actually see the lean codes coming when i watch the mpg needle slowly creep from about 32-34 to about 28 during constant throttle, I floor it and it goes away again , thus keeping the cel off.

The icv was replaced at 84k, the ccv at 84k, and a brand new intake boot also at 84k. The vcg was replaced by me at 107k along with spark plugs. I have along with 2 different mechanics sprayed all the hoses for vacuum leaks, nothing . And the maf sensor reads what it should.

Anyone have any insight on this ? Started this a while ago on bimmerfest but nothing came out of it.
 

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Have you checked the condition of your DISA valve, sounds like it maybe seriously clogged with oil. I had a similar issue with my bimmer which looks like a vacuum leak but turned out to be a clogged non-functioning DISA. I replaced the DISA and my gas mileage returned as well as my drive-ability... Just my two and a half cents worth...
 

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Discussion Starter · #3 ·
My sister doesnt live too far from you....

And i have not. I will do that today, got to change the oil in my dads 330ci first -__-. I'm just afraid of pulling it off and the flap being screwed.
 

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My sister doesnt live too far from you....

And i have not. I will do that today, got to change the oil in my dads 330ci first -__-. I'm just afraid of pulling it off and the flap being screwed.
Taking out the DISA takes about 10 minutes.

Remove two airbox 10mm bolts.

Remove 6mm hose clamp from MAF sensor.

Pull out airbox

Use T40 torx socket to remove two DISA bolts (may need short extension w/ wobble or flex joint)

If your flap is loose, just disassemble the flap and leave it off til you get a new one.
 

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Ok so I have been having this problem since I bought the car. It's intermittent, i randomly get the P0174 and I believe 0171 lean mixture both banks along with missfire on low fuel. It's only when the car is driven for a few miles at low rpm. However if I drive the car spirited the cel goes away. I believe I can actually see the lean codes coming when i watch the mpg needle slowly creep from about 32-34 to about 28 during constant throttle, I floor it and it goes away again , thus keeping the cel off.

The icv was replaced at 84k, the ccv at 84k, and a brand new intake boot also at 84k. The vcg was replaced by me at 107k along with spark plugs. I have along with 2 different mechanics sprayed all the hoses for vacuum leaks, nothing . And the maf sensor reads what it should.

Anyone have any insight on this ? Started this a while ago on bimmerfest but nothing came out of it.
Many possibilities:

- Intake air leaks
- Pre cat O2 sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the MAF. If the problem persists a pre CAT O2 sensor may need to be replaced. Its a process of elimination.

BTW. If you are going to take the DISA out use a magnetic screw driver. The bottom screw has zero clearance around it and you can't get a hold of it. Its a bitch.
 

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Discussion Starter · #7 ·
Ok disa valve works just finished washing my bloody hands. Interesting there was alot of grimey sandy stuff, everywhere inside the manifold.

Thank you for the replies.
The entire airboot is new. No cracks, sprayed brake cleaner on all hoses, no leaks

Airfilter is K&n so that's good. I know its going to come up but this was all happening before the panel filter install. MAF is clean as well.

Fuel filter is a good question . I personally have yet to change it. The car has 116k on her.

When i worked for a dealer (imports ;) ] all the mechanics couldn't figure it out but were curious as to why the short term fuel trim was always screwed unless the maf was clean, used a dis to diagnose it but sensor was always clean and functional.

O2 sensors still working. How would it be intermittent though ???

Once again thank you for the replies!!!
 

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Ok disa valve works just finished washing my bloody hands. Interesting there was alot of grimey sandy stuff, everywhere inside the manifold.

Thank you for the replies.
The entire airboot is new. No cracks, sprayed brake cleaner on all hoses, no leaks

Airfilter is K&n so that's good. I know its going to come up but this was all happening before the panel filter install. MAF is clean as well.

Fuel filter is a good question . I personally have yet to change it. The car has 116k on her.

When i worked for a dealer (imports ;) ] all the mechanics couldn't figure it out but were curious as to why the short term fuel trim was always screwed unless the maf was clean, used a dis to diagnose it but sensor was always clean and functional.

O2 sensors still working. How would it be intermittent though ???

Once again thank you for the replies!!!
An O2 sensor is not like a light bulb which either works or it doesn't. An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gasses leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts. The sensor does not begin to generate it's full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor will not spend any time at 0.45 volts. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an "illegal" value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution. The O2 sensor is constantly in a state of transition between high and low voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison may not be accurate. Going for as burn up might burn off any such pollutants leaving the O2 sensor working as it should until the pollutants build up again. So it is not entirely unlikely that O2 sensor issues might be intermittent.
 

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Suggest you look over the first link below in my signature.

Most likely rotten rubber hoses and/or some sort of crankcase air leaks.

The most often overlooked problems are the CCV lower oil return line, the fuel pressure regulator vacuum hose as the fuel filter and the vacuum hoses under the rear of the intake.
 

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Discussion Starter · #10 ·
An O2 sensor is not like a light bulb which either works or it doesn't. An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gasses leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts. The sensor does not begin to generate it's full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor will not spend any time at 0.45 volts. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an "illegal" value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution. The O2 sensor is constantly in a state of transition between high and low voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison may not be accurate. Going for as burn up might burn off any such pollutants leaving the O2 sensor working as it should until the pollutants build up again. So it is not entirely unlikely that O2 sensor issues might be intermittent.
That was very useful information. And interesting. But last time I had the scanner hooked up we , the mechanics and i , all agreed they were operating woth in range ( did ibsay that right ?) And concluded it wasnt the pre or post cat o2.
 

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Discussion Starter · #11 ·
Suggest you look over the first link below in my signature.

Most likely rotten rubber hoses and/or some sort of crankcase air leaks.

The most often overlooked problems are the CCV lower oil return line, the fuel pressure regulator vacuum hose as the fuel filter and the vacuum hoses under the rear of the intake.
Ccv and hoses were replaced. I shall find the **** I got from the dealer as far as paperwork, and i actually had them give me the old parts.

As far as the fuel pressure vacuum line? Where would one find this ?
Maybe air getting in the fuel lines would make it look as if there is an air leak somewhere else yes ? And would throw lean mixture codes. And the missfire on low fuel.
 

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No air getting in fuel line due to fuel pressure regulator vacuum line.

The fuel pressure regulator is part of the fuel filter, under the drivers side front floor board.

The other end is from the F connector on the upper intake hose to the firewall.

DISA & DISA O-ring can be problems as well as other crankcase air/vacuum leaks.

I see you removed your DISA and cleaned it, but did you check it for proper operation and notice how well the larger seal most likely DID NOT seal well?

All this info is in the DISA section in the first link in my signature.

Might as well read the 2nd & 3rd links in my signature as well.

Really should keep an eye on engine coolant temp and inter lobe fuel transfer as well.
 

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Discussion Starter · #13 ·
Yes when I removed the disa I checked the flap it was tight, and spring loaded as well. And there was a Orange seal stuff that maybe could have been the gasket ??? I see there is information about a pin.... Since my disa still is operational and in working order could this pin still fall out ???

I read your posting , I felt like a 10 year old looking at a new bike.... Lots of useful information in there.
 

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My only concern with your above post is that the gasket is green in color, not orange which may mean you need to replace the gasket with a new one. A DISA valve gasket leak can cause a vacuum leak, lean fuel condition as well as higher oil consumption and higher fuel consumption issues. I know my DISA valve issue caused all of these issues in my bimmer.
 

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Be careful about the DISA for a number of reason.

The vacuum diaphragm in the DISA can and does fail causing a vacuum leak and the DISA not to function correctly.

Also be careful about the main DISA O-ring color.

The 323/328 has a green, serviceable O-ring that you can get at the dealer or use the Felpro replacement that is for a Ford thermostat.

The 325/330 has an injected, orange, silicon seal as an O-ring. The problem is this injected silicon has little to no compression strength and it will not spring back easily as is ages, so when the plastic intake manifold cools off and contracts and the DISA cools off and contracts you very likely have a large cold start vacuum leak. If the vacuum diaphragm is blown, things are even worse.

When you remove the DISA if you have no resistance to remove the first 1/4" inch or the DISA just falls out, you need to replace the O-ring.

On the 325/330 you actually need to scrape out the original injected silicon to install the new O-ring. The 325/330 uses a special order 3/32" thick O-ring that is not readily found at locate auto parts stores.

Suggest you read the DISA section VERY carefully in the first link below in my signature, this is all covered in detail.
 

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I have the exact same problem, and I did 90%+ of what has been suggested in this thread. Intermittent lean codes coming up with the exact driving conditions OP described. "Intermittent" is the key word here. This automatically eliminates vacuum leaks, as they would result in persistent codes rather than intermittent.

Only things I haven't done are:

1. Install new MAF (otherwise cleaning and testing done).

2. Intake manifold gasket.

3. Injector O-rings.

I believe the problem is sensor related (due to being intermittent), so 1 is more than likely the cause. My car runs fine otherwise and I average 26.1 mpg mixed, so MAF is waiting to be replaced for the time being.

I have documented what I did so far in a thread. You might want to check it out.


Sent from my SGH-I997 using Bimmer App
 

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Discussion Starter · #17 ·
Orange * not green I'm sorry about that. It was difficult to get the whole thing off. It was my first time doing so as well. I will order the gasket for the disa at the price might as well. I'm still curious as to the pin that is often talked about, the disa isn't broken but will the pin fall out ? It's dark and cold so i will take a look at the underbelly of this beast in the morning for the vacuum and fuel lines.
 

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Discussion Starter · #18 ·
I have the exact same problem, and I did 90%+ of what has been suggested in this thread. Intermittent lean codes coming up with the exact driving conditions OP described. "Intermittent" is the key word here. This automatically eliminates vacuum leaks, as they would result in persistent codes rather than intermittent.

Only things I haven't done are:

1. Install new MAF (otherwise cleaning and testing done).

2. Intake manifold gasket.

3. Injector O-rings.

I believe the problem is sensor related (due to being intermittent), so 1 is more than likely the cause. My car runs fine otherwise and I average 26.1 mpg mixed, so MAF is waiting to be replaced for the time being.

I have documented what I did so far in a thread. You might want to check it out.


Sent from my SGH-I997 using Bimmer App
Ahhh objectors o rings. Iv tested those, came up nothing... Iv probably wasted 15 bucks on brake cleaner in a year on testing all of this . I believe I have seen your thread , i remeber the car.
 

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The DISA pin will not fall out as long as the DISA butterfly is in good shape, even then it may not fall out until you actually remove the DISA.

The DISA needs respect!!!!

Here's the bottom line, CEL popping with lean codes at idle is 95% vacuum leak, CEL popping with lean codes while cruising is likely a bad/wrong/counterfeit MAF, fuel pump/filter.

If you have a scan tool that captures freeze frame data and the DME supports it, freeze frame data can be very helpful to narrow down the issue(s).

Also suggest you read my comments in this thread on additive vacuum leaks - http://forum.e46fanatics.com/showthread.php?t=957638
 

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Discussion Starter · #20 ·
Ok sooo. Recently got a new toy. Torque. Nowww my car reads everything fine. Except my LTFT are both stuck at 11.7 and are constant. My o2 sensors read as they should amd the maf reads well I assume. Im at a loss.

Sent from my SPH-L710 using Bimmer App
 
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