P0174 only code

electric130 · Oct 11, 2010

I've spent the last 2 hours searching, and most results were both a p0171 and p0174. I only have the p0174 code. with both codes, everyone was saying things that would apply to both banks. so what would allow the car to run perfect, yet throw the p0174 only code? i read somewhere that the intake gasket was split into bank 1 and bank 2. so if that's true, then there could be a leak on the bank 2 gasket. no one seems to think the O2 sensor could be bad. i swapped the plugs on the pre-cat sensors and the p0174 code went away, engine ran rough, and i had pending codes:

P1343 Misfire Cylinder 1 With Fuel Cut-off (BMW)
P1345 Misfire Cylinder 2 With Fuel Cut-off (BMW)
P1347 Misfire Cylinder 3 With Fuel Cut-off (BMW)

so that would be bank 1 reading off bank 2's sensor. what i was hoping to see was the p0174 go away and then p0171 come up, which would point to a bad sensor. i plugged the sensors back in correctly and the car ran smooth again.

i've checked the vacuum lines i could without tearing the engine apart. i had the lower intake boot off a couple months ago and it was fine. with the split behavior the car is showing (bank 2 lean or misfires bank 1) and that there's no common link in the faults, it makes me want to steer away from the common vacuum leaks that would affect both banks.

i need some input. what else could cause this split performance?

wdeerfield · Oct 11, 2010

ive gotten this code a couple times and it ended up being a dirty MAF and i had to clean my air filter. Code has been gone for over a year now.

electric130 · Oct 11, 2010

did you have the p0171 code too? air filter was changed 2k miles ago.

also, i did the spraying carb cleaner around all the vacuum lines and intake and the RPM's never changed.

immigrant · Oct 11, 2010

Check the intake elbow for crackings.

electric130 · Oct 11, 2010

i already did :read:

bishop1977 · Oct 11, 2010

you might have a fouled o2 sensor...nice thing is, i ordered 2 precat oem bosch from fcp for 125 shipped for both

electric130 · Oct 11, 2010

what made you decide to order 2? did you have fault codes?

shanneba · Oct 11, 2010

Since you are only getting P0174 lean on bank 2 (cylinders 4-6) you could check the O2 sensor voltage with diagnostic software like a GT1/DIS Autoenginuity etc.

There is an air distribution part on the top of the intake manifold. It is held on with 4 screws, are they all tight?
It also has 6 o-rings that seal it to the intake manifold, if there are leaks in the back three you may only see a lean code on bank 2.

http://www.realoem.com/bmw/showparts.do?model=BD53&mospid=47713&btnr=11_2879&hg=11&fg=40

You could check the intake manifold bolt torque values. Maybe the rear are not completely tight? Could be the rear gasket for the manifold.
You could spray some intake cleaner around these areas with the engine running to further troubleshoot the leak possibility.

electric130 · Oct 11, 2010

i already tried spraying around the intake manifold and it didn't change the RPM's. the O2 sensor is only $70 for a Bosch and it's in-stock locally, so i might try that since it's fairly easy to get to. if that doesn't fix it, i'll look at the intake gasket.

bishop1977 · Oct 11, 2010

well i had 171 and 174 then it went away but i also have 88k miles with a supercharger...so changing 2 is better than changing just 1...

electric130 · Oct 11, 2010

well, i was just out running some errands and the SES light went out. i had gone about 20 miles, got back in my car from my last stop and the light went out after starting the engine. not sure wether to be happy or nervous it's going to come back. :hmm:

P0174 only code

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