First symptom was that my car was misfiring just as i pressed the gas and was transistioning to part throttle cruise. The car ran fine with 30-100% throttle and had good power. Then my check engine light came on. I took it to autozone to pull the code and it reads P0430. Catalyst efficiency below threshold bank 2.

Possible areas

1. Gas leak on exhaust.
2. Three-way catalytic convertor
3. Open or short in heated oxygen sensor circuit
4. Heated oxygen sensor

So I reason the misfiring had something to do with it which isn't listed.

I asked the guy at autozone if there were other codes present and he said no.

I did buy some new plug wires for the car and had not replaced them yet. So I changed those thinking my problem will be solved. Wrong. Car still had the same symptoms and I was really beginning to rack my brain. (I should've inspected the plugs but I had to be at work soon and didn't have time.) Bank 2 is cylinders 4, 5, and 6. If the coils or wires or ignition signal were bad it would cause bank 1 to misfire also since they share the same coils and wires between the banks. So I narrow it down to plugs or injectors on cylinders 4, 5, or 6. Being that spark plugs are easier to diagnose than injectors, I pulled number 6 and 5. Number 6 looked normal but I replaced it anyway.

Number 5 spark plug was the culprit. It had carbon tracks on the insulator indicating the insulator was cracked and grounding the plug out at certain rpms. I replaced it with a new one and took it for a test drive. Problem solved.

Moral of the story. Just because a code is thrown doesn't necessarily mean the listed solutions will fix the problem. Otherwise I would be spending thousands for a new catalytic convertor.

Now I just need to fix that damn low idle problem.

 

Excellent.

When I used to live in Mexico City, I would add two other culprits, bad gas (high sulfur, leading to bad combustion) and climate (25% less oxygen and also this affected combustion).