I will appreciate any help or advise guys! I just bought 2004 XJR. Every time I put gas in the car CEL comes up with P0171 code. After I clear the code, car drives fine for 4-5 days until next stop at the gas station. Checked for leaks, cleaned MAF sensor. Gas cap seems OK. What is it???!!!

 

Probably a vacuum leak in the intake system. I can also be caused by a bad or just dirty Mass Air Flow sensor or a leaky EGR valve or air pipe to it.