Bung on s13 ka24de downpipe
 

So, I've searched for days and in multiple forums and even went to the dealer and can't find an answer. There is a threaded hole on my stock downpipe that is really close to the steering column. It actually faces almost directly at it. I thought at first it was for an o2 sensor but when I tried to plug one in, the hole was too large. I've seen this hole welded shut as well. I will post a picture when I can lift the car back up. But does anybody know what goes in there or if I can just plug it up. If you know the size of the plug that would save me as well.

Thanks in Advance.

I'm guessing this is where the EGR re-route too?
Weld it up.

I added a pic. Is that the only option? I feel threads in there, maybe a plug would suffice?

EGR. You can find a bolt to fit that shut

Correct me if I'm wrong, the egr tube is above the o2 sensor. And you can see both from a top view of the engine bay. The hole I'm referring to can pretty much be seen only from the bottom of the car. I took the picture of the unplugged hole being under the car. I also have a picture of what I believe the egr is(being hooked up as well, while the original hole, the first pic, is still unplugged).

So it was a hole for the AIV. Thanks for the help everyone.