kakress

Got the codes read for my 2000 Civic (the most basic model possible- automatic trans)- P0505 (IAC circuit condition or idle too high/low), P0141 (Secondary H02S12 circuit heater malfunction), and P0135 (A/F Sensor 1 heater system malfunction). I've been told "your cat is melted- it needs to be replaced." and "there's no way to tell if your cat is bad without removing it." I have virtually no experience with cars and no tools or garage. I don't know if I should replace the O2 sensors and IAC valve and see if it clears up the problem. I have noticed a loss in power, but it doesn't ever reach a plateau in speed (can still go 70+ MPH). The car does shake sometimes and dies every once in a while when I come to a stop. Can anyone offer advice on my first step in getting this problem fixed? I guess I'm wondering if I should replace the cheaper parts first before getting into the more extensive stuff. I will really appreciate any help, as I am stressed out and at a loss. Thank you!