420 2zz-ge Help

Not that 420! I've been battling a P0420 code in an 03 Matrix XRS for the past year & inspection time is drawing near. The car has 190k on it and in the past year I've done two smoke tests and replaced the following;

Purge Valve Solenoid. Up & Downstream Denso O2s. (Replaced the upstream twice) Direct Fit Catalytic Converter. Welded 2 leaks in the front pipe near the O2. Air intake clamps were replaced as the old ones weren't securing it well enough. Coils were tested as well. Even tried some ethanol stabilzer product.

I get about 100-200 miles before the code comes back and the car feels like it's running with 1/2 the miles it has. I'm beginning to think it wants to be a VW. Now, what experience do you all have with this code and what should my next point of action be?

Was it an OEM cat replacement?

They very commonly go bad if lower grade fuels are used, SWMBO had to replace a cat in her old XR because of this at about 80k because of this, also remember both cats can be suspect as well, good luck!!

In reply to JtspellS:

Not OEM Toyota but aftermarket direct fit. The PO had hacked in a universal. Running 93 in it as well.

I have nothing to add, but am interested in all 2zz-ge knowledge.

Toyotas are very picky with aftermarket cats, unfortunately.

try this. It worked on my mother's Grand Prix.