Toyota Repair: 2000 Toyota Solara check engine lite

Question
Had a P0420 and P0330 code and Ted Ritter suggested I "front converter directly after the exhaust manifold"

Before I replaced the front converter, I replaced the EGR valve and the EGR transducer and cleaned the port at the bottom of the intake throttle valve and cleared the check engine light.In a short period od time the light was back on. Then I went ahead and replaced the front converter as suggested and I replaced the next exhaust pipe with catalytic converter. At this time also replaced the air cleaner intake tube and resonator as these were brittle and had cracks in them. this managed to last the longest, 2-3 weeks but now the light is back on with a P0420 code (catalyst system efficiency below threshold bank 1)

As of now I have done nothing with the O2 sensors or the EGR vacuum solenoid. I had another suggestion to reposition the throttle position switch by removing it's bushing  to gain a slight adjustment, which I have not yet done.

I would appreciate any suggestions on the next best option to try and correct this. Not sure what the likelihood is of a bad ECU.

Thanks, Joseph Caroccia

Answer
I would recommend that you have the cat converter tested using a diagnostic scantool that can read live data from the A/F ratio and O2 sensor, this would indicate if the converter is working or not and also test the O2 sensors for proper operation by reading the voltage values, you could also elect to just replace both sensors but it does not have a specific code for those, it's possible that an aftermarket converter if used did not meet Toyota's requirements.