Hello! There are several reasons why this code may set.
First, if the filter is dirty, it usually doesn't make it run lean, unless the filter has allowed dirt to reach the Mass Air Flow (MAF, often called an Air Mass Meter) sensor, or if the air filter is really oily, it may have also contaminated the MAF sensor. If this is the case, you can sometimes get lucky and carefully clean the end of the MAF sensor with brake cleaner.
Also, since you do have a cold air intake, make sure all of the duct work to the throttle body is intact and all the clamps are tightened. Also make sure any hoses that were hooked up to the original air intake, still have a place to go (you can't have any unconnected hoses or nipples).
Vacuum leaks are common with this engine, and the BEST way to check for them, is to install a smoke machine. I know most consumers won't have one, or even have access to one, but its truely the best way.
Another common issue is the Crankcase vent system. To tell if its failed, you can usually remove the oil fil cap and feel an excessive sucking from the oil fil (sometimes the engine will die if the vent system is bad when the cap is removed)