p0171 code truck running rough

I have a 2002 2.4L 2wd with the manual. Last november I had the cylinder 3 spark plug strip out and needed to insert a helicoil. I removed the head from the block mainly to avoid getting tap shavings in my cylinder, and also to inspect my internals as it was bought used with 120k. After a good cleaning it went back together smoothly, but I've had a lot of different trouble codes since. Most of which have been evap related, and after changing the purge valve the only code left is p0171 A/F too lean. I've visually inspected all my vacuum lines and haven't found any obvious leaks. everything is connected back correctly. at one point I had a cylinder 1 misfire so i changed the injector and fuel filter but I still have a lean code.

 

Could be the Mass Airflow Sensor (MAF). Might try cleaning and/or testing that.

 

How do I check a MAF do I check for resistance?

 

Here's some text from the service manual on the MAF (see pic below). This is from the 2000 FSM:

1. INSPECT MAF METER RESISTANCE Using an ohmmeter, measure the resistance between terminals THA and E2.
Temperature -> Resistance
at –20°C (–4°F) -> 13.6 – 18.4 kΩ
at 20°C (68°F) -> 2.2 – 2.7 kΩ
at 60°C (140°F) -> 0.5 – 0.7 kΩ

If the resistance is not as specified, replace the MAF meter.

2. INSPECT MAF METER OPERATION
(a) Connect the MAF meter connector.
(b) Using a voltmeter, connect the positive (+) tester probe to terminal VG, and negative (–) tester probe to terminal E2G.
(c) Turn the ignition switch ON.
(d) Blow air into the MAF meter, and check that the voltage fluctuates. If operation is not as specified, replace the MAF meter.
(e) Turn the ignition switch OFF.
(f) Disconnect the MAF meter connector

 

when i checked resistance on the sensor I had about 3.5k ohms between terminal E2 and THA. The voltage test read out normal.

 

It is about 30 degrees farenheit outside right now I'm not sure if that would cause resistance to read that way.

 

Seems ok for 30F, but hard to tell. Might be worth taking the MAF inside and letting the temp stabilize to get a more accurate reading closer to the 68F in the chart. If that reads ok, could be a leak in vacuum lines like you originally stated.

 

I'll try that but I'm really considering a smoke test at this point

 

I'd clean the MAF sensor first. If you need another MAF - try getting one at a junk yard for cheaper

 

Okay it's been a while but I cleaned an already pristine MAF sensor to no avail. the evap purge solenoid in the engine bay has been replaced, and I found a large vacuum leak coming from under the bed. That hose got replaced. after smoke testing and fixing that vacuum leak i still have extremely rough idle and a terrible misfire under 2500 rpms. the only other smoke leak i have now is from the gas cap and i have trouble codes p0171, p0440, and p0446. i dont think a slightly leaking gas cap would cause my truck to stall at anything under 2500 rpms