Engine Performance problem
2000 Toyota Avalon 6 cyl Front Wheel Drive Automatic 135900 miles
Last week the Check Engine light came on. The code was P0420: Catalyst system efficiency below threshold-bank1/ probable cause 1) Air leak in exhaust before rear HO2S(Heated oxygen sensor)Bank 1; 2) AF sensor error; 3)Fuel system fault; 4) Faulty catalytic converter.
The car is not running rough or idling rough indicating a stopped up catalytic converter, but this week especially has started really sucking gas. Where would I have my mechanic start? I cannot afford a " process of elimination" at his time being a disabled widow.
ALSO: Just before I took possession of this car about 2 months ago the rear struts and mounts were replaced. I am still hearing a " clunking" noise like something is loose when going over a rough spot in the road. I've been told everything under there is tight and not a tire iron loose with the spare. What else can I have them check for?