Cat Converter Plugged On 1.8L ?

Just replaced the upstream O2 last summer, now downstream failing.

Can't go over 45 uphill, downshift causes bogging.

idle exhaust is not very forcefull, but it is a 4 cyl...

No whif of oil or gas in radiator.

No trouble filling tank, tho a bit of gas smell when starting.

oil burning is going down a couple oz,s a month, since we started changing it less. No choclate milk there....

Water resivoior not dropping noticebly, even in desert sw.

200k miles, but not a lot of long trips on this vehicle. Big altitude gains/losses as daily driver. 3500 to 5000 ft a day.

Dealer charged us a 1k last year trying to fix. No fix. i replaced O2 , ran pretty good till now...

2001 le, 1.8l

I understand there is a computer/software bug in these cars, and there is a big downhill coast/engine brake happening in afternoon after starting, which would increase rich fuel loading, but am suspecting Cat now...

Just checked records.

Dealership changed O2, AFM, plugs, wires, injectors, coilpacks, All in the last year, problem not fixed.

nearly 4k, and still havnt found the prob. Ouch.

Possible it is a clogged cat - backpressure test with a probe or if you notice a considerable amount of blowby, then that could be the case.

But it takes a LOT to clog a catalytic converter. Exhaust leaks can also cause the ECM to misread O2 values, causing the engine to run too lean or too rich - which will affect power.

Not completely understanding what the dealership changed or why: O2 sensor (upstream), plugs, injectors, coilpacks - I can see as possible culprits, hopefully they gave you the old parts back. Wires? What wires - spark plug wires? I hope not, your car doesn't have plug wires. AFM? Not on a Corolla - maybe a BWM or similar. Unless they meant the MAF sensor - those can be cleaned, don't have to replace them.

I'm surprised they didn't check the VVT-i system - as that would cause a lot of headaches if it wasn't running as it should. If the valve overlap is not right with the VVT-i, could get stumbling, low power, bogging at high speeds, etc.

Transaxle issues are another possibility - especially if the car works OK, just doesn't want to get up past a certain speed. This would also point to that funny downhill engine braking you are seeing, should be doing that unless the fluids are too cold. Could be a bad shift solenoid or transaxle.