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Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 01-27-2013, 02:31 PM   #1
MCM97
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Car throwing P0171 and P0174 codes at highway speeds

I've search and thought I was on to the solution but it doesnt appear so.

Yesterday I did my valve cover gasket and changed spark plugs and in the process broke the plastic hose that leads from the manifold to the crank case. I replace it no problem, buttoned up the engine and everything was going great until I got up to highway speeds for 30 min and the CEL threw. Pulled the codes and it was P0171 and P0174. Cleared them and drove to dinner last night. On the way home about 20 minutes into the drive the CEL threw again, same codes. So this morning I started doing the troubleshooting:
- Check the MAF - car runs normal at idle but when you unplug the MAF the RPMs come up and it settles finally. Plug the MAF back in and the car misfires, seems to want to die and finally catches.
- Pulled the dipstick with the car on. No change in idle
- Hit the usual suspects with carb cleaner. No change in idle.

Overall the car runs great but I keep getting these damn codes at highway speed 20-30 minutes into the drive. Does anyone know the next step or what to replace/check next??
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Old 01-09-2014, 12:44 PM   #2
johndonahue
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Car throwing P0171 and P0174 codes at highway speeds

I was wondering if you ever figured out the problem? I have checked everything, replaced everything; MAF, fuel filter, manifold gasket, VCG, boots, vacuum lines suction jet pump, DISA, VANOS, cleaned the ICV, and I still get the codes at highway speeds. Car is not throwing them at speeds less than 60 mph. But get up to 70-80 mph and codes come back. One poster suggested a soft fail of the MAF or of the fuel pump. Since I have already replaced the MAF, I was wondering whether the fuel pump can really cause lean codes? I really am at wits end.
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Old 01-09-2014, 02:15 PM   #3
the_ace
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My 325 was throwing those two codes only at highway speeds after a good run, new fuel pump fixed it! For the money (70) and half an hours tinkering its worth changing it anyway as if its original it will be due for renewal soon enough anyway!
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Old 01-09-2014, 06:16 PM   #4
johndonahue
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I'll try it. I know it seems like I have spent a lot of money chasing things, but I have 228,000 miles on it, 104,000 since I bought it. Everything I've fixed was due anyway. I'll change out the pump and report back. Thanks.

Last edited by johndonahue; 01-10-2014 at 01:28 PM.
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Old 01-22-2014, 11:17 PM   #5
johndonahue
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Lean codes

This might get long, but I wanted to share everything I did to eventually rid myself of the dreaded P0171 and P0174 lean codes. I have a 2001 530i with 228,000 miles on it.

At first, I noticed that in the morning I had some rough idle. Eventually it progressed to the point where it was really rough. Misfire codes and lean codes showed up after the SES light came on. I started looking on the internet to diagnose the problems.

First thing I did was pull the DISA valve. It was shot. The diaphragm was loose; the pin would come out, and the gasket was flat. Ordered a new one and put it in. Got rid of the misfire codes and car ran great, but still had lean codes.

So next I bought a new MAF sensor. Bought an aftermarket one off ebay for about $50 and installed it. (More on this later). Still had lean codes.

I then built my own smoke machine and smoked the engine. Smoke came out of several places: valve cover gasket area and from the sucking jet pump. In trying to look at the sucking jet pump, I learned that it is a fragile part as I broke it trying to get it out of the clip on the engine. Bought a new sucking jet pump. In trying to figure out a way replace it without removing the intake manifold, I tried a brass coupler in the hose. However, I ended up breaking the connection to the intake manifold when I pushed too hard trying to get it fully into the hose. I then had to get another manifold (used off ebay). So I ended up taking off the manifold anyway. In the course of replacing the manifold, I installed new intake manifold gaskets and replaced all of the vacuum hoses underneath and on the back of the manifold. The vacuum hoses were disintegrating. Despite all of this, still had lean codes.

I had previously replaced the CCV less than a year before (< 25,000 miles), so I did not figure it to be the problem. I inspected the CCV and hoses, all were good. When I replaced the CCV, I also replaced the intake boots and throttle body gasket. All were still good, so they weren't the problem.

I replaced the valve cover gasket and redid the VANOS seals since I was in there. While doing so I also replaced the pre-cat O2 sensors.

Still had lean codes. Car ran great, smooth, acceleration good, no smoke, no problems, except for the lean codes. The lean codes only showed up when I was driving at highway speed. If I drove around town, keeping it under about 50 mph, no lean codes. Only at highway speeds. Couldn't figure it out.

Researching again, I replaced the fuel filter/pressure regulator. Lean codes still there. Then replaced fuel pump. Lean codes still there.

I decided to smoke the engine again. Smoke came out of the area of the DISA valve, even though I had replaced it with a new one. When I pulled the DISA valve off, I noticed that the red silicon gasket was already messed up. That gasket is junk. I had already bought a replacement gasket and decided to use it. I cleaned off the red silicon gasket, put the new one on and reinstalled it. Resmoked the engine. No leaks anywhere. But I still had lean codes.

Not sure where to go and about to give up. Started looking again and saw some folks talking about aftermarket vs. OEM MAF sensors. Having nowhere else to go, I decided to reinstall the MAF sensor that I had taken off early in the process. I didn't even clean it. Voila, no more lean codes. Lesson learned is that when people talk about using only OEM MAF sensors, they were absolutely right.

I obviously had a bad DISA valve, and I must have had vacuum leaks in other places. The work I did on the other parts of the engine: VANOS, O2 sensors, VCG, vacuum line hoses, suction jet pump, fuel filter, fuel pump, all needed to be attended to as preventive maintenance anyway, considering the age of the car and mileage, so I don't regret doing them, even though the majority of them weren't causing the lean codes.

Hope this helps. I hate that a new OEM MAF sensor costs over $300. Tough to swallow without being sure it's the problem. But if I have to replace the MAF, I will go OEM. And I will never put a DISA valve in without replacing the gasket first.
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Old 01-23-2014, 12:04 AM   #6
SeanC
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That's pretty much where I'm at. Replaced everything but MAF. Same issues, no codes around town, but they are back on the highway. I know the problem is with MAF, but I gave up on it since the car idles fine and has decent power. Maybe I'll do it sometime.
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Old 01-27-2014, 08:24 PM   #7
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Quote:
Originally Posted by johndonahue View Post
This might get long, but I wanted to share everything I did to eventually rid myself of the dreaded P0171 and P0174 lean codes. I have a 2001 530i with 228,000 miles on it.

At first, I noticed that in the morning I had some rough idle. Eventually it progressed to the point where it was really rough. Misfire codes and lean codes showed up after the SES light came on. I started looking on the internet to diagnose the problems.

First thing I did was pull the DISA valve. It was shot. The diaphragm was loose; the pin would come out, and the gasket was flat. Ordered a new one and put it in. Got rid of the misfire codes and car ran great, but still had lean codes.

So next I bought a new MAF sensor. Bought an aftermarket one off ebay for about $50 and installed it. (More on this later). Still had lean codes.

I then built my own smoke machine and smoked the engine. Smoke came out of several places: valve cover gasket area and from the sucking jet pump. In trying to look at the sucking jet pump, I learned that it is a fragile part as I broke it trying to get it out of the clip on the engine. Bought a new sucking jet pump. In trying to figure out a way replace it without removing the intake manifold, I tried a brass coupler in the hose. However, I ended up breaking the connection to the intake manifold when I pushed too hard trying to get it fully into the hose. I then had to get another manifold (used off ebay). So I ended up taking off the manifold anyway. In the course of replacing the manifold, I installed new intake manifold gaskets and replaced all of the vacuum hoses underneath and on the back of the manifold. The vacuum hoses were disintegrating. Despite all of this, still had lean codes.

I had previously replaced the CCV less than a year before (< 25,000 miles), so I did not figure it to be the problem. I inspected the CCV and hoses, all were good. When I replaced the CCV, I also replaced the intake boots and throttle body gasket. All were still good, so they weren't the problem.

I replaced the valve cover gasket and redid the VANOS seals since I was in there. While doing so I also replaced the pre-cat O2 sensors.

Still had lean codes. Car ran great, smooth, acceleration good, no smoke, no problems, except for the lean codes. The lean codes only showed up when I was driving at highway speed. If I drove around town, keeping it under about 50 mph, no lean codes. Only at highway speeds. Couldn't figure it out.

Researching again, I replaced the fuel filter/pressure regulator. Lean codes still there. Then replaced fuel pump. Lean codes still there.

I decided to smoke the engine again. Smoke came out of the area of the DISA valve, even though I had replaced it with a new one. When I pulled the DISA valve off, I noticed that the red silicon gasket was already messed up. That gasket is junk. I had already bought a replacement gasket and decided to use it. I cleaned off the red silicon gasket, put the new one on and reinstalled it. Resmoked the engine. No leaks anywhere. But I still had lean codes.

Not sure where to go and about to give up. Started looking again and saw some folks talking about aftermarket vs. OEM MAF sensors. Having nowhere else to go, I decided to reinstall the MAF sensor that I had taken off early in the process. I didn't even clean it. Voila, no more lean codes. Lesson learned is that when people talk about using only OEM MAF sensors, they were absolutely right.

I obviously had a bad DISA valve, and I must have had vacuum leaks in other places. The work I did on the other parts of the engine: VANOS, O2 sensors, VCG, vacuum line hoses, suction jet pump, fuel filter, fuel pump, all needed to be attended to as preventive maintenance anyway, considering the age of the car and mileage, so I don't regret doing them, even though the majority of them weren't causing the lean codes.

Hope this helps. I hate that a new OEM MAF sensor costs over $300. Tough to swallow without being sure it's the problem. But if I have to replace the MAF, I will go OEM. And I will never put a DISA valve in without replacing the gasket first.

excellent information, I am also at the same stage because the MAF seems to be the most expensive single thing to replace with oem, will report back after the correct one has been reinstalled ! (I kept the old original one)
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Old 02-08-2014, 09:38 AM   #8
ROBY328CI
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You also need to consider bad gas , but anyway you didn't specify where you have these lean codes under load or idle speed ? You read FREEZE DATA on your scanner when the error code came up ? Please don't replace sensors on your cars until you are testing with scaners etc

Last edited by ROBY328CI; 02-08-2014 at 09:40 AM.
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Old 02-08-2014, 10:23 AM   #9
SeanC
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Quote:
Originally Posted by ROBY328CI View Post
You also need to consider bad gas , but anyway you didn't specify where you have these lean codes under load or idle speed ? You read FREEZE DATA on your scanner when the error code came up ? Please don't replace sensors on your cars until you are testing with scaners etc
He says at highway speeds
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Old 02-08-2014, 05:12 PM   #10
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Sorry Sean C i didn't read the title )
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Old 02-08-2014, 05:22 PM   #11
ROBY328CI
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I have the same problem but only at idle speed.I think i have a bad CCV because opening filler cap the engine rpm change dramatically.I saw a guy on youtube with same lean codes solved changing the gas station Check also ScannerDanner channel on youtube

Last edited by ROBY328CI; 02-08-2014 at 05:39 PM.
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Old 02-19-2014, 09:44 AM   #12
ZackE46
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Im also having the same lean codes thrown. I recently had 4 cylinder misfires (yes! 4!) due to an extreme vacuum leak from a CVV hose and fixed all codes expect for the lean codes. Is it worth the money to go ahead and buy a MAF or should i just replace small common gaskets first? Can't seem to figure out the problem. I've done valve cover gasket, new plugs, new hoses on CVV, checked DISA Valve, and checked for more vacuum leaks (couldn't find any). Also do y'all think maybe the O2 sensors are bad? and maybe thats causing the lean codes. I had a misfire for about a month before i had the money to fix the problem
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Old 02-21-2014, 12:12 PM   #13
ROBY328CI
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If you have a scanner you certainly can test o2 sensors , maf etc .. individualy.If your o2 go under 0.2 V and over 0.8 V they are good.I'm curious what values give your maf on idle speed , at 1500 RPM and at 3000 RPM because i recorded mine , and after clening it , gives me 2.4 g/s .I have 328ci from 2000.
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Old 03-01-2014, 09:28 PM   #14
Jay DD 007
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did you check the egr valve? since it's activated mainly at highway speeds maybe it could be letting a little too much in. just a thought
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Old 03-02-2014, 12:59 AM   #15
ROBY328CI
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I resolve it changing ccv .All tubes were broken. Instantly no more lean codes, fuel trims from +27 % goes to -11 % at idle speed
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Old 03-03-2014, 01:13 AM   #16
DyeBmw
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For my codes I have done the following
1.new ccv especially breather hose was cracked under engine cover
2.new disa
3.new o2 post and pre cat
4. Thought maf sensor was bad but was still fine, don't buy aftermarket maf sensor
5. Fuel pump
6. New intake boots
Fought to solve these codes for 2 months and finally passed inspection and no engine light. Good luck


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Old 03-26-2014, 08:32 PM   #17
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I'm been searching a bunch on this the past two weeks or so. However in my case I feel like it would be too much of a coincidence if I have one of the normal causes for these. I replaced my intake air filter that was in there for about 30k miles (I know shouldn't have waited that long) with a K&N air filter. A few days later I got the lean codes p0174 and P0171. Cleared it with the cheap obd2 scanner/bluetooth adaptor I have. next day or so SES light came on again but had 3-4 misfire codes as well. cleared it and next day or so just the lean codes again.

The only other things that I did recently were sprayed some engine degreaser/cleaner and within a minute or two sprayed it all off, I'm wondering if something got knocked loose from the pressure? or possibly cleaned build up off of somewhere now exposing a leak?

or

Put some seafoam in with about a 1/2 tank of gas maybe 7-8oz of seafoam with 8 gallons of gas (as per instructions on seafoam bottle)

Any thoughts on this?
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