Emissions Question

[jw11432]

So, a week ago I went to get my sc300 inspected and it failed. Here are original numbers:

First number is standard/passing, second number is what my car read

HC - 111/19

CO - .61/.07

CO2 - X/12.5 for these two, the X represents there is no requisite figure for passing.

O2 - X/2.5

NOX - 773/2004

dilution - >6.0/12.57

Having seen scores like this before, I thought it was a bad cat again. So I replaced the cat. Here are the consequent figures after a new cat:

HC - 111/20

CO - .61/.20

CO2 - X/14.7

O2 - X/.1

NOX - 773/938

dilution - >6.0/14.9

They retarded my timing a bit and it brought all the figures down to where I could pass (barely, but my O2 went up from .1 to .2)

Now, I know that I have a small leak in my intake tube after the MAF, so theres some unmetered air likely getting in. Secondly, one flange on my cat has only one bolt holding it on, cuz the stud broke off, so I'll probably just get a tiny c-clamp on it and call it fixed. Oh, and I use regular gas instead of premium (i know i shouldnt, but money has been super tight) but I read that lower octane fuel can cause higher NOX readings.

If there is anything I'm missing, as in if it's likely that there are bad O2 sensors, or EGR valve is clogged/dirty (pcv is relatively new), I'd appreciate all input. I imagine addressing the known issues is the obvious place to start though.