had one in 3 times for this fault code and P0171, first time it had a split breather hose, 2nd time was the diaphragm PCV valve (you can blow through it when faulty) and last time which was nearly 2 weeks ago i replaced the MAF meter with a Bosch one and all seems ok.

Make sure you reset basic settings as you'll not notice any difference until you do. This will reset fuel trims as well.