From my experience, if you drastically change the air intake system it trips your O2 (oxygen sensor) that plugs into the air intake to tell the computer how much airflow you are getting.
That is why tuners are made for vehicles that people put modifications on... they plug in to the ecm (computer) to the vehicle and "tune" or make changes to the computer so it updates it to your current modifications so your engine will run right.
Essentially the error is coming up because the computer thinks you are running a stock air filter, but really you have upgraded and the sensor is recognizing that.
The other possibility outside of tuning the ECM (computer) of the vehicle is plugging a special O2 sensor in place of the stock O2 sensor to trick the computer so it doesn't bring that stupid error message up.
We desperately need a tuner for the Tundra, but nobody makes one. That is why our trucks will not run right with modifications. Now that this is cleared up.
Back to the topic...
