My 2000 Sentra is showing a PO171 "System too lean - bank 1" code and the shop I took it to is telling me to replace the Mass Air Flow sensor but I don't think that's the problem. I've had to replace an oxygen sensor before (2 years ago) and had recalls completed on my car for a faulty crank position sensor (about two years ago as well.) My SES light started to come on for a few days and go off for a few days, with a tiny bit of sputtering while accelerating up a hill (around 2000 RPM) before I took it to the mechanic, but now it's having more trouble than before. When I start the car for the first time in the morning, the car starts fine then won't accelerate and sounds like it's going to stall then doesn't. It goes a few feet, then has the problem accelerating again (press the pedal, nothing happens). If I stop and wait a minute for the engine to warm up, it accelerates just fine and doesn't give me the problem for the rest of the day (even when starting after 2-3 hours off.) How do I know if it's an oxygen sensor, the fuel filter, fuel pump, or MAF sensor? Should I change my spark plugs/ have a tune up early? (They're platinum tipped and according to the owner's manual last 105,000 miles.) Do I need to start replacing less expensive parts and work my way up, or is there a test I can do to find out exactly the problem? Thanks!

I replaced my MAF sensor last year,
because the car stalls pretty bad (like everytime when I let go of the gas).
anyway, took it to the dealer. They wasn't so sure either, so the mechnic started to change parts (spark plugs, air filter...etc)
then finally he realized it was the MAF sensor by replacing it.

That was one stupid mechnic, but anyway....c if u can talk to the dealer and let them check on the MAF sensor for u.
It costs like....$500....not cheap

MAF most likely cause. Nissan uses very crappy suppliers for parts especial since the current CEO came along. He is a cheep Bastard. Saw it a thousand times when working for Nissan. The dealer will try to blame an aftermarket air filter.

sputtering sounds like the MAF sensor, the cold start issue sounds like an o2 sensor, id replace the sensor first, its only like 50 bucks at napa, the maf however is pretty expensive, id try to get that done under warranty

Did you find the solution to your problem. Because i am also having the same problem and i changed the MAF sensor on my car but it did not do anything it actually kind of made my car worse. let me know if you found a solution thanks.

Once your car runs like crap for a while the computer "learns" this. when the problem is fixed you need to clear the self learn. do this by disconnecting the battery cables overnight. Hook up in the morning and see if problem is gone. by the way, the air flow meter is a very common problem for a p0171 code.

Thanks for the advice on the battery. I have the same problems with my 2000 sentra, but also have a gasoline smell in the car when I drive. I replaced the oxygen sensor the other day with no luck. If I disconnect the battery over night and still have problems, am I also looking at the MAF as a solution?