Yep....997 airboxes are the way to go....that is what we found too.

 

OK, I'm convinced, after I clean up the stock box (covered in Arizona dust) and make sure I have all the parts, it's going back in.
Is it even worth it to try and sell the K+N? I presume nobody here wants it, maybe ebay.

 

Some people like 'em so give it a shot....

 

Re-installed the stock box today, luckily the PO saved all the correct hardware. Couple of things don't add up though, first, there is a small port on the rubber boot before the throttle body (see red arrow) I don't know here that goes to.
Next, the MAF appears to plug in backwards, (see red circle) seems as though the PO put in the cheapest one he could find on Rockauto, time for an upgrade? Bosch good to go?

 

It can be helpful to give your year and model when asking for tech support. My '99 intake boot is different than your pic so I would just be guessing. As far as your MAF sensor plug being backwards, it was discussed a couple of days age here. Good luck!

 

I think you have a Tiptronic airbox, as those have that little port by the throttle body. Is your car a Tiptronic?

 

Car is not a tiptronic, and the air box came with the car, along with the stock springs and various bits.
I've plugged the tube for now (forever?)

Thanks, Greg

 

Idaho is right, the 2002 and up Tiptronics are the only ones with that extra port, it goes to a venturii to help the Power Brake Booster during low manifold vacuum event. It must not do a lot of good even for the Tips, because Fabspeed plugs it off also on their CAI kits.

So your Original air box/hose is somewhere else..

 

Someone probably got tired of buying the Bosch MAF only to have it fail. That's due to being covered in oil, and fouled from the open element air filter, and the oil they treated it with.
There's NOTHING good that come from these intakes. I am not saying this because I am a purist, I am saying it because I have 18 years of direct experience proving they are inferior to a stock airbox.

 

Drove it for 50 miles last night, and codes came back. Frustrating.

So, plan going forward, is replace upstream O2 sensors (again, looks like all 4 are the same, cheapest available) with Bosch units, and replace MAF sensor, then I can establish a baseline with new parts.
I'll report back next weekend with results.

Thanks everyone for helping me understand this car,

Greg.

 

Am I the only one, who's never "oiled" a K&N or any other fabric type filter before?

 

I never oiled the one that came on my 2003 Mini Cooper S when I bought it used.

By the way, if one is after a better engine sound, resonator or red cap mod can be done with the stock airbox and filter. And reversible. Sounds great at open throttle. Sounds a tiny bit better on a Boxster S, but still worth it on the 996.

 

My .02... I have a 2001 996 C2 Cab with approx 87,000 miles on it. I purchased it about a year ago and one of the first mods I did was to install the IPD Competition plenum, 82mm GT3 throttle body and a K&N CAI. I also got a tune installed and swapped the exhaust for a complete Top Gear system including the 200 cell sport cat x-pipe. I also replaced the original MAF sensor and the O2 sensors both pre and post cat. Very happy with the sound, especially from 5K to 7K rpm, but I felt like I lost some low end torque and smoothness as the engine winds up.

So today I re-installed the stock air box, but with the silicone tube (air box to TB) and rubber cap (to block off the air box muffler) from IPD, along with a new BMC air filter. Took it for about an 80 mile drive over a mix of expressways and two lane roads and I gotta say that overall the stock airbox with the above mods is superior to the K&N set up. Smoother response, no hesitation on the way up and still sounds awesome at WOT. No discernible change in the butt dyno IMHO.

I ended up wrestling with the new silicone air pipe a lot more than I expected since it is very stiff and frankly seemed a bit too long, but I was able to get everything seated and tight.

So I guess I now have a K&N CAI to put on ebay...

 

People are fooled all the time by this. There's nothing "cold air" about it, you still induct engine bay temperature air, or even hotter air than stock. I have collected that data with stand alone dataloggers, starting back in 2008.
Sometimes on a dyno the aftermarket systems will make more power... That's because of how the tests are performed, and the environment of most test cells.

So the next guy can install a handicap onto his engine.
When we remove them, I blow them up.

 

That tube is for Automatic transmission OR X51 manual engines. Yours is a 2000, so couldn't be X51. The PO must have purchased the intake second hand and not realized it was for an auto. I would just buy the smooth intake elbow and get rid of that piece all together. It won't throw a code and will sound a lot better by cutting off the air muffler.

It's a cheap part. Can find it here