Hi bro, really admire how helpful you are to others! been reading your post regarding the P0171 code and I've been having the same problem, replaced spark plugs and the MAF sensors and transmission fluid, cleaned the VTC sensors and the cam-shaft position sensor with electrical cleaner. O2 sensors are not faulty because if they were failty they would throw a code. Car throws the code (P0171) ONLY at hard acceleration! If I drive the car for 100+ miles without getting harsh on the gas pedal it won't throw any code. Suspecting the brake booster o-ring you mentioned but I'm facing difficulties in finding the o-ring. If you can please explain in more details where exactly is this o-ring and what else should I inspect.Thanks in advance.
G35S 5AT 2007 with 180 miles on the engine.
MODS: stillen GEN 3 intakes,, Z1 intake manifold, OBX LTH, Invidia Cat-back, Uprev tune, Stillen oil cooler, Mishimoto thermostat, BC racing coilovers, GT-spec strut bar and Eibach sway bars.

Having problem with my 2003 g35 coupe has 134,000 miles and my ABS,slip light and VDC lights come on after driving and applying the brakes and what happens is all my brakes lock up, but I pull my brake line from the booster to the engine and all of a sudden my brakes release and was wondering does that brake line have a check valve in it and I changed my pads and flushed out my brake fluid and changed out my brake booster could this be my abs block or an electrical problem or is it my master cylinder need help ASAP and thanks

Thanks for the reply....can't figure why they estimated this repair so high. I took this car in for an oil change and had them look into this leak and that is what they told me...disappointing...I have trusted them so far....I'm wondering if they realize the fix can be as simple as you mention. Maybe I'll check with a Nissan service dealer and ask them for an estimate. I appreciate your answer.

Sigh... I took it to the dealership and they did hydrocarbon test and its got gas in the coolant system that's mean a blown head gasket....fml but when I took to the first mechanic shop did they the test too and they didn't find anything so now I'm lost... Only way to find out now is get block test myself... Or trade this sucker in... Too bad I really love these cars man...