yet another p0171 problem. Intake gasket is good.

[Canker]

This car has 200k miles on it. I've already replaced the intake gasket, old one looked fine. I've cleaned the maf and ran techron through it. I don't see any obvious vacuum leaks but I'll look harder in the morning. http://repairpal.com/OBD-II-Code-P0171-and-P0174That page says a good way to check the maf is to look at the barometric pressure on your scan tool. Do these cars have anything to read the barometric pressure. I'm running torque on my adroid phone as my scan tool and it has options for barometric and intake manifold pressure but nothing shows up for either of those. I do get something for mass air flow rate for what it is worth. I don't want to just throw parts at this thing so any ideas? I should also ad the car seems to run fine to me other than bad gas mileage. The check engine light doesn't come on very often either.

[Canker]

Got a chance to check for vacuum leaks and found nothing. Car pulls a steady 18 on my vacuum gauge. Also checked the PCV while I was at it and it seems to be working fine.

[circuitsmith]

Check for leaks between the maf and throttle.Check fuel pressure.There is no barometric pressure sensor on this engine.

[Salsa Guy]

It's odd that you have a lean code and have bad fuel MPGs. Perhaps your upstream O2 sensor is bad and showing lean but really rich. That could account for both issues. The O2 sensor is considered a "wear item" and in this case you may want to change it out. The cost about $50 for an OEM direct fit. Denso is a good brand but make sure it's for the correct year. They changed sensors for the FWD/DBW models in 05.

[Canker]

Most of the things I've come across say it isn't the o2 sensor. That the computer does a diagnostic on the o2 sensor to make sure it is ok before throwing this code. If the o2 sensor doesn't come back ok it throws a code for the o2 sensor instead but I don't know. I just found out I can see my fuel trim numbers using the torque app and what little I understand about them they seem fine. I don't know if it is showing long term or short term numbers though. They are right around 0% plus or minus a few and mostly hanging out in the minus a few % but they aren't going 10% more either way. Maybe it has fixed itself lol. Might just need to watch them longer.I need to do more research tonight at work. I'll check the fuel pressure in the next couple days.

[Salsa Guy]

Like any sensor to a computer if you get garbage in you get garbage out. Normally if you are really running lean you should get GREAT MPGs. That's the part that makes me wonder.Yea the computer does some check on the o2 sensor buts its very basic. It has no way of confirming the signal. These O2 sensors are "narrow band" and takes a minor issue to throw measurement off. It could be a corroded connection to it causing a voltage drop. Goodluck

[circuitsmith]

If it's lean enough to cause misfires MPG could suffer, but the loss of power would be felt.

[Canker]

I bought the paid version of torque last night and it does show short term and long term fuel trim. It mainly looks like they contradict each other. One will go -5% and the other will go +5% but I haven't plaid with it much yet. During my drive home I did get a few 10+% spikes in the long term mainly when I would first take off hitting the gas but I never saw anything over +17%. Check engine light hasn't come back on since Sunday. I took a long drive to visit the parents and it came on twice within 3 miles of leaving the house but I cleared it both times. I'm going to wait till it comes back on to see what the computer is doing before I go throwing parts at it.

[thejustman85]

I bought the paid version of torque last night and it does show short term and long term fuel trim. It mainly looks like they contradict each other. One will go -5% and the other will go +5% but I haven't plaid with it much yet.

My wife's 05 Vibe's fuel trims behave similarly. (she also has a p0171)
Maybe I don't really understand their operation but it doesn't seem like they should be opposed to each other especially on a fresh session(i.e. if long term trim is just an average of short term trim).
I'm pretty sure her long term trim is causing her CEL and p0171. It never drops below 4.7% and it frequently gets to around 20%(even though short term trim goes positive and negative -20% to 10%).
Did you ever resolve your p0171?

[frankiemenz]

Try cleaning yor MAF, use MAF cleaner aerosol spray, not carb cleaner! Dirt build up on element and cause positive fuel trims, and P0171. Intake gaskets are common too, cleaning maf is very easy and inexpensive and recommended 1st!