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lots of codes el 2004 c4

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I have a 2004 c4 that I purchase 3 days ago it has been sitting for 8 months and it is running a little rough now yesterday a bunch of codes come up! can anyone out there help p0151 - p0126 -

p0131 - P0171  - P0174  - P0300 -  P0301  -  P0302  P0303 . I HAVE PUT ONE NEW TANK OF GAS IN AND RAN THRU IT . its still running rough and the front end is shaky at 75mph  must be flat spots on the tires .


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Can't help with your codes but if vibration increases in frequency as speed increases, then perhaps flat spots. If the vibration comes and goes within certain speed ranges (generally multiples of each other) then it's more likely a balance issue. 

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Are you sure it's p0126? I saw p0125 and p0128 and no p0126 in the WSM

p0131 bank 1 O2 sensor voltage too low

p0151 bank 2 O2 sensor voltage too low

p0171 bank 1 too lean at idle

p0174 bank 2 too lean at idle


Sounds like to me issues with the O2 sensors and/or wiring and that tripped the lean code and misfires. This will need further diagnosis with a Porsche scanner and basic electrical troubleshooting.


As the first step, you may want to reset all the codes and drive the car longer (assuming the car is still drivable and not struggling) and see what codes come back.

Edited by Ahsai
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Agree with Ahsai.  Clear the codes by disconnecting the negative battery lead for several minutes, or using your code reader.  Given that it has not run in 8 months there could be some stale gas.  Put a bottle of Techron in the fuel tank.  Then go for an easy drive.  Try to maintain an even speed over some distance (several miles).  See what codes may come back.  The P03XX are misfires.  They could go away with some consistent running with a warm engine.  Otherwise you may need to replace spark plugs and check your coils for cracking.

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Flat spots usually go away, if the tire has good tread and it is not too old and dry rotted.  It may drive you crazy for awhile at certain speeds.  If the tires are older than 3 years, you might consider new tires and balancing in the near future.

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