Now the P0171 appears on my car. I searched related solutions on the google and found the P0171 and P0174 always appear together on general car, but my car just appear one, what happens?

 

the P0171 code is very likely caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.
I had the problem with my Corvette after installing a cold air intake,it took 10 heat cycles for the computer to learn the new CAI.

 

yeah, first thanks your reply, I agree with your view, that may be intake leak, but someone told me that oil pressure also may caused this code, right?