Well, I tested the downstream 02 sensor and it's well within range.

Looks like it's the cat getting clogged up. Can anyone recommend a good bolt-on aftermarket catalytic converter? I don't need anything that will last 15 years like a OEM Honda cat, but at least something that will last 4 or 5.

Turns out there's a missing bolt on my exhaust manifold, which is throwing off my air/fuel mixture. The gasket is marked with black soot in two spots.

What's a fair price for a mechanic to drill it out and replace the stud?? Should I replace the one stud or go ahead and replace all of them?

Most of the cost would be labor, IMO. I would assume one hour? You would have to call and get quotes to find out.

I am of the opinion if it ain't broke, don't fix it. You may want to put a bit of anti-seize on the threads to prevent the nut from rusting on the threads.

Hmm, which nut are you referring too?

The stud is broken off inside the head and none of it is protruding from the manifold. My dad cut if off and taped a new hole.

IIRC, there is a two-way threaded stud that goes into the cylinder head. The manifold goes over the studs, then a nut is what holds the exhaust manifold to the cylinder head. This is based on my 95 EX that I sold more than a year ago.

I'm not sure if your accord is an LX, DX, or EX. The LX/DX may be different.