Update on removing secondary air filter & K&n filter install
 

My wife has noticed only slightly increased mileage. it went for 16.9 to about 18.9. She drives a lot of interstate miles with a bunch of running around in town. So about 2 miles a gallon and this has stayed the same cause she does not drive any different before or after the install. This has been on 6 full tanks of the same brand of fuel.
So at 20,000 miles a year(yes)
from 16.9 @ 2.98 gallon a cost of $3526
to 18.9 @ 2.98 gallon a cost of $3153
For a yearly savings of $373.
Yes i know it will vary due to me driving it every blue moon(heavy footed) and other factors but if we just got half that savings its still more than the cost of the mod done.

Prius which gets about 45 mpg driving like we would use it would cost

$1324 for a savings of $1829 a year. Problem is I cannt find one of those bastareds that they will sell even at sticker.
Not trying to start any post war just wanting to post some helpfull info on MY personnel experiances with the mod mentioned.

I did the same with my 4Runner and just drove down from Portland to Los Angeles where I got 23.6mpg. Thought that was pretty good. That is with removing the secondary and with a K&N flat panel.

but with the increased oxygen doesn't it burn more oil with the increasd oxy available, thus increasing build up in engine over time

You would assume so. I had checked my oil before I left LA to Portland and again when I left Portland to LA, and with 6000 miles on that oil it was still suprisingly clean. Id say at this point that with the removal of the filter it has not made an impact on the oil's integrity.

I'm not sure what you mean by that. Why would there be more oxygen?

If the vehicle is truly being driven the same, the airflow is the same, and so is the oxygen content of that air.

The only way there could be more air flow is if the throttle is open far enough to take advantage of the decreased restriction. And that decrease in restriction would probably only be a benefit when the throttle is at or very near wide open.

After all, with the throttle partially open, for instance about halfway, the throttle plate is the most restrictive part of the intake. No modification other than forced induction or a bigger throttle body will cause more airflow at half throttle.

And keep this in mind: With increased airflow comes more fuel. As airflow increases, the fuel injection system senses this and increases the fuel flow to compensate. The fuel mixture should be the same both before and after the modification because of this. There's no more more oxygen available to burn any oil that's there than before.

Assuming that the rings or valve guides don't wear more after the modification for some reason, there would be no more oil introduced into the combustion chambers. So again, there would be no more oil burned than before.

And if anything, you would want unburned oil to burn. Unburned oil in the combustion chambers causes deposits.

help
 

please, some more info on this subject gentleman

Dont know what they talking about buring or using oil. Oil in my wifes is fine.
Update on the mileage. Its going up 19.4 mpg. And she drives the same route every day. Course she has her Eye on the Prius now that she is paying for the gas.

Its official. I now have 1500 miles on removing the stock air filter, replacing it with a drop in K&N panel filter, also removed the charcoal secondary filter. Results? 22.3mpg! Not bad for a Runner?! Especially when you consider Im in LA traffic.

still getting about 22mpg with mod.

Have you noticed any difference in the idle? I've heard that the secondary filter evens out airflow to the MAF sensor. Works the same as the throttle body screen in other vehicles.

I stare at that filter every time I've opened my intake up and wondered if it really needed to be there....

---Ron

I have not had any issues. It runs just fine. And my wife would be the first on my ass if there was any issues with HER 4runner.

If anything, it might idle a tad bit lower in the RPM's when you take it out. There really is no need for that thing.
Think Ive said it before, but if you were to put on a cold air kit, or a short ram kit, it would be taken out either way. I still cant beleive that Im getting the kind of gas mileage around LA in this truck. Besides, even if it does anything, I personally am just going to sell it in a few years and get another new one.

where exactly is this secondary charcoal filter located on an '03 4.0 ??
i have a K&N cold air kit installed but never heard of this 2nd filter.

Its in the intake part, once you pull the main air filter out you will see it. Its on the engine side of the intake. Not sure a 03 would have it in there. Also not sure how your intake set up is right now. But the filter is in the housing that is bolted to the top of the engine.

How do you remove this stuff? Did you have a post on it?

i dont think there is one. if there is it's in the old airbox thats sitting in my storage

The thing is really easy to get out. I have been averaging 22.5 mpg now (assuming that is fairly good for the 4runner) that it has been taken out. That is on at least 5k miles now. No adverse effects either. Try it.

I finally got around to removing my secondary air filter a few weeks ago, just to see what would happen. I noticed absolutely no increase in power or fuel economy.

Came Out Fairly Easy
 

Drilled out the little plastic rivets that hold it in place. Wish I would have remembered my right angle attachment.

I didn't have to go through that much trouble. I just took a screwdriver, and between prying and tugging, i had it out in less than a minute.

I still have not noticed a difference in either power or fuel economy.