K&N Cold air intake vs OEM air filter box

TLDR: Stay away from aftermarket cold air intakes and just stick with the OEM assembly. MAF doesn't know how to interpret the uncontrolled Turbulent air flow and will create a poor air fuel ratio among other problems.

I bought my 2002 AC tundra about 2 Months ago. One of the two previous owners had put in a K&N Cold air intake, I'm guessing the first owner probably because the filter was horribly dirty and not maintained at all likely by the second owner who didn't know it needed to be cleaned/oiled or replaced. Additionally one bracket that stabilized the pipe was missing, I'm assuming the person who put it in just wanted it to be louder and the shaking filter did just that.
Needless to say since owning this Truck it has idled very rough sometimes below 500rpms surging intermittently. It has very limited power, horrible gas mileage, and would shake and vibrate at any rpm. It would intermittently make noise from the throttle body opening and closing via the ECU presumably when the MAF thought it wasn't getting enough air.
I knew I would eventually replace the intake after I solved its problems running so I just bought a new filter for the time being (waste of 100$). In the process of trying to help it run correctly I thoroughly cleaned a very dirty throttle body and MAF. I Replaced all spark plugs, PCV valve, numerous hoses and searched for vacuum leaks with propane. I even bought all new O2 sensors as a wild guess.
A few weeks ago I was able to find the connecting pipe at a scrap yard for 30$ and today received the filter box for 30$ from eBay. Today I finally got that cold air Intake out and replaced it with the cleaned OEM box and fresh filter. I relearned the throttle after reconnecting the battery and after about 2-3 minutes it smoothed out. It has never had so much power, it's never idled this smooth and at normal rpms, It doesn't vibrate at all and I am so happy to have finally solved this.
My understanding is that the OEM box controls the airflow so that the MAF is receiving a consistent Laminar flow that the ECU is capable of interpreting. This is essential for the ECU TO compute the correct air fuel ratio. The Cold air intake puts the MAF very close to the opening where the air flow is turbulent and so the ECU can never truly gauge the exact air flow it's getting.

 

• Skip "cold" air intakes and aftermarket cold air/oiled filter crap. You know, the stuff K&N, AEM, others sell. Dyno testing on popular YouTube channels proved Toyota's OEM filter produces more overall power than aftermarket kits, while also filtering particulate more aggressively, keeping the engine cleaner. Those kits may work on other engines, but Toyota really dialed things in on our trucks to eek every last bit out. Those kits may make more growl, feel more torque-y, but dyno charts tell a different story. The only dependable way to squeeze out power or pep semi-inexpensively w/o forced-induction is with long-tube headers, or re-gearing.

Not my quote. This comes from the MEGA THREAD

Also, Welcome! Black Texas trucks are Best

 

The irony is now you are actually drawing cooler air from the fender well!

I am curious, did you happen to check the maximum air flow the MAF reported (g/s or cfm) from the K&N compared to the OE setup? I suspect the value would be the same between the two, but that is just speculation.

 

Some of us are drawing in air from outside the fender well

 

I know, I don't think I understand the intention behind the design of the CAI. And I don't actually have a nice enough scan tool to read values like that unfortunately

 

Here’s a recent photo I posted elsewhere here. Notice the outside air temp and intake air temp on the Scangauge: