I keep on getting the check engine light on my petrol i6. I have taken the car to the dealers 3 times and the error code is P0171. Dealer found no apparent fault and downloaded new software 86.90.89. Strange thing is that the engine light comes on and then goes off in 2-3 days time. After a week or two, reappears for a couple of days and goes off. This cycle continues for 2-3 months… Does anybody experienced this or similar problem?

This is a copy and paste from the Net kostaschrys

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My 2008 LR2 had DTC P0174 - System Too Lean (Bank 2) which caused the Check Engine light to come on.

Researching common causes, the first problem suggested was a vacuum leak. If you can hear a hissing sound while the engine is running, then you've found a rather significant leak. But a very small leak won't be found by human hearing. You'll need to take it into the shop and have them perform a smoke test.

However, the next most common cause is a dirty Mass Air Flow (MAF) Sensor, which is attached to the engine side of the air cleaner housing. I removed mine and it did not appear dirty to my eyes, but the delicate filaments in these sensors are very sensitive and can be impacted by microscopic dirt or pollen particles. I cleaned it using MAF Cleaner Spray I purchased at my local auto parts store. Since cleaning it, I cleared the code and it has not come back on, so this was likely the problem.

A few more notes about the MAF: It is a very fragile and expensive component so you have to be careful while handling it. Youtube has a couple videos showing how they are removed and cleaned on other vehicles. In my case, I could not easily remove the wiring plug from the MAF and I did not want to risk breaking anything. So I just left it plugged in while cleaning it over the engine after laying down a large plastic garbage bag below it to cover everything else. Also, you MUST use special electronics parts spray to clean it. The cheapest is sold as MAF Cleaner Spray in most auto parts stores. Finally, my LR dealer told me that LR does not clean this item as one of its routine services. Their policy is to replace it, not clean it, which seems odd to me because it is generally recommended to be cleaned on other vehicles every time the air filter is changed, about every 30K miles. The part alone costs over $150, so I would try cleaning it before replacing it. BETTER looking half of the famous Twinlanders
The wanna be other half - http://www.freel2.com/forum/member-carriec.html

Thanks Slaneydore,
I think I will clean the sensor, and then we will see if it will go back to normal. The only thing I don't understand is why to cause only the p0171 and not the p0174 as well.

Good advice above. Only thing I would say is that if you need to replace the maf then only consider buying a genuine part and no copy part.