Replaced the upstream O2 sensor and cleared the codes. All codes cleared except the P0171 code. After some searching, this codes seems to be a pain to fix. I'm guessing (since I had the whole intake apart to install the valve covers) it's a vacuum leak that I have not found yet. Any other suggestions? I plan on replacing the majority of my vacuum lines. Hopefully this helps.[/QUOT
I hope this helps, you would be totally surprised how often it is something simple causing a problem.
When you said it went away and then came back, a light went off in what's left of my brain, LOL.
It sounds to me like the "Oxygen Sensor" on the incoming air supply, right after your air filter is dirty. Listen and clean it this way using what I tell you.
Get a can of CRC electronics cleaner from just about any parts store.
Do NOT try to save a buck or so by using any other parts cleaner like break cleaner, laundry cleaner, anything else, I'm dead serious!
Now, unbolt the housing (to the oxygen sensor) right after where the air cleaner is. If unsure about where/what it is do a search on the Internet.
Once the housing is unbolted lift it out and shine a light down the tube, you will see a sensor. Looks like a bubble of plastic around a couple of wires about 1/2 the size of your little finger nail.
DO NOT STICK ANYTHING DOWN THERE AND TOUCH IT!!!
It will break and they aren't cheap!!
Now, use your can CRC (per label instructions) to spray the hell out of the sensor and and housing interior, I usually use about 1/3 of a can (can is about $5.00).
Turn it upside down and let it all drain out(BE CAREFUL, Highly Flammable) let it dry for about 30 minutes. Bolt everything back up. That's it.
Clear all codes!
The following is things that you should know:
Do this with a COLD engine (flammable stuff, CRC), don't forget this!
Do this twice a year or when you're having problems.
To totally clear codes, disconnect battery for 30 minutes.
Total time to do this (after the first) is about 10 to 15 minutes.
If it's not the answer at least it will cure a ton of other problems.
Let me know.
Um, wut? What you are referring to, is NOT an oxygen sensor. The O2 sensors are on the exhaust system measuring exhaust gas mix. By the description you gave…it seems you are referring to the Air Intake Sensor or AIT. That would have nothing to do with the code the OP is dealing with. I could be wrong though…...
Sounds like kigmob is talking about the maf sensor. Cleaning the maf sensor will probably be beneficial.
I'm leaning towards a possible vacuum leak after taking the intake all apart. Try getting a can of starting fluid and spray it around vacuum line connections. The engine will idle up a bit if the connection is leaking.
Good luck OP! Keep us posted. . .
I will keep you guys posted!