P0171 code help needed

So my check engine light came on. I had replaced o-rings on 2 fuel injectors and it was working fine. Drove 2 hours to a party, sat there for a few hours, then drove back. It came on as soon as I got home. I changed the spark plugs the next day, I was going to anyway, and it went off for a while. Since then, I've cleaned the MAF sensor, inspected the intake system for cracks or leaks, reset the ECM, and run through a full tank of gas with fuel injector cleaner....any suggestions what to try before I start replacing sensors? I was told it could be the coolant temperature sensor, O2 sensor, MAF sensor, or the MAP sensor. If there's nothing else to try I'm going to go through and test, then replace them in that order

 

Check PCV valve and the PCV rubber line for it for cracks, stuck open etc..

 

Have you looked up the code?
Here's what this guy did
http://www.tacomaworld.com/forum/1st-gen-tacomas/86601-po171-obd2-code.html