P0171 System too lean? Possible bad fuel???

[mark01348]

Hi guys,
     Just wondering if any has had any issues after using a particular fuel at all? On 7th July my came went into limp mode and EPC came on. Dealer was unable to diagnois a fault from the codes that were stored and the main one being P0171 - System Too Lean (Original topic: http://www.mk5golfgti.co.uk/forum/index.php/topic,31824.0.html)
So yesterday same thing happened. It turns out on both occasions my misses has just put 95ron petrol in the car from a particular garage. I've had the codes cleared and filled it with super unleaded and the car is now fine. Would lower octane fuel really cause such a big problem? When EPC is on car has no boost at all 
I've got a 300 mile journey tuesday and I know if I go to dealer all they would have done is clear the code and the car will drive fine.

Thanks,
Mark.

[bacillus]

Find someone in your area with a vcds to scan your car ascertain what code is stored and if any futher action is needed.

[mark01348]

I paid dealers who did guided diagnostics but cleared code and because the fault didnt return they said the cars fine so im reluctant to take it back to them. My EOBD scanner keeps saying P0171 - System Too Lean

[bacillus]

This is what ross tech says about that code.
http://wiki.ross-tech.com/wiki/index.php/16555/P0171/000369

[mark01348]

I'll ask them to check MAF readings to see if in tolerance friday but in the meantime is there a fuse for ecu which will clear codes or will battery reset work? (Should the need arise)

Thanks for your help

[bacillus]

Normally if your maf is faulty, if you disconnect it the the car should idle better.

As for code clearing, temporarily disconnecting the battery should work but be prepared to see a few check lights in the dashboard once you restart. These lights should disappear after driving a short distance so be warned.