Something simple as a PCV can cause problem. Good catch

 

yeah, mine turned out to be a cracked vacuum hose. my mechanic just happened to catch, actually was the first thing he thought of....after me independently trying numerous things for days before i gave up and took it to him

 

My wife found a receipt from Autozone.. the one they print out that shows the code and what might be causing it. Its P0171, and its dated December of 2008. Apparently I was battling the P0171 for longer than I realized.

 

did the code go away?

 

I just got this code last night too! I do have a kn intake and headers. First I'm gonna try injector cleaner and maf cleaner. I'll also check for that hose. Any other suggestions?

 

P0171 on a gs4 is coming from the driver side cylinder bank. Thats where the PCV valve is. It was a split in the PCV hose that caused mine. Since thats the side farthest away from the air intake, it could be related to the air intake. There are three small hoses that come off the air filter/resonator. You might want to check those too. One in particular, coming off the back of the resonator is notorious for breaking off. Could also be the fore O2 sensor on that side too.

I'll be interested to hear if its the PCV hose.

 

Thanks Fasted!

I'll check that out after work today. I cleared the code and so far it hasn't popped back on. I did notice the K&N intake has an AEM dry filter on it and someone oiled it!! Maybe I'll clean the filter and the MAF too just in case?

 

I had this code come up right after refueling. I noticed a huge release of pressure when removing the fuel cap (car was still running). The light was on when I got in the car. After about 50 miles, the light is now off.
I've refueled with the car running before and it hasn't done this, maybe it's just due to the extremely high temperatures recently?

 

why are you re-fueling with a running engine?

 

when your checking for vacum leaks it help to have a spray bottle with water. If you wet each hose you will be able to hear the leaking one suck in the water.

 

yea, I'm trying to figure that out too?

 

I checked all things and rechecked, then i used a smoke machine and i found that the leak was from intake manifold by #7 cylinder. Removed and cleaned top and bottom intake manifold. Make sure You change all intake gaskets including secondary air pump which is located in the back of the top portion of the intake manifold. Problem solved. I was fighting this problem for couple months. Even the dealer could not tell me why i'm gettin P0171 code.

 

replace intake gaskets and it will go away. I learned that hard way doing that to my lexus.