my 2002 SF 2.4 showed high CO and high hydrocarbons. I have no CEL and no codes. A while back I did clear a MAF code. But the car was running fine and it did not throw another code. They put a sensor in my pipe, did not hook up their computer to the car.

What are the most common problems...please.

 

I'll answer my own question.

Google helped me with probable causes. The MAF sensor was the one I zeroed in on.

Youtube showed me how to clean it.

Afterwards, it seemed to run better, but not THAT much better. But the emissions retest showed that the MAF sensor was the problem. I don't believe it had ever been cleaned, but I bought it used so...

Anyway, it passed, I spent 4 dollars on a can of spray and an hour on the internet.

All's good.