Hey Scotty! Huge fan, always watching your videos.

I have a 2011 Hyundai Equus. Mileage: 125420mi. Automatic transmission.

After not driving the car for a while, the car was being used again so they could prepare to sell it. Well, the check engine light came on while the car accelerated poorly. The car had a misfire detected so the spark plugs were changed. This is what happened BEFORE I was called to look at the car. Immediately, I checked the codes. 

4 confirmed codes: p0335 p0307 p0300 p0303

5 pending codes: p0307 p0420 p0301 p0300 p0303

I started by looking for any vacuum leaks using live data and some carb spray. Nothing.

I called my mentor and asked him what I should do. He said change one of the coils and see if it fixes it. So I switched coil on cylinder 5 & 6. The codes p0335 and p0420 went away.

So I switched all the coils. The remaining codes are: p0300 p0301 p0303 p0307.

The car was taken to the dealership. (The end of the warranty on powertrain was coming up.) They replaced the crankshaft position sensor and they told my client that they put a camera into the exhaust and stuff was coming out of the catalytic converter. So they wanted to replace the cat and the o2 sensor.

What should I do?

Thanks for any pointers. I never thought to look into a v8 Hyundai but here we are! ha! Cheers!