CEL Code: P0174

So I have thrown a CEL. CODE P0174 - Engine running lean.

A couple weeks back I removed the secondary filter. Everything was fine for a few days then the CEL came on. The next day it went off and seemed normal again. Then again today the CEL came back on, took it to Auto Zone and read the code. I'm assuming that the engine is running lean due to the removal of the secondary filter with the increase of air.

It seems weird that sometimes the light comes on and sometimes it's off. I wonder since I live at almost 6000ft if the altitude has anything to do with it, I also use 85 octane. Could I completely discconnect the battery to get the MAF sensor to re-adjust to the new set up?

I'm trying not to worry all that much as I have a TRD CAI coming this week.

What should I do if it is still throwing a CEL after the intake is on. Would that be a warranty issue since it is a Toyota Part?

Confused...

 

I would try the disconnecting battery trick to reset the code. Leave it disconnected for about 20 minutes and then connect it back up. If the code doesnt come back in the near future, I would say you are clear.
As to what is causing it, I dont know, could be a combination of all the things you mentioned.