Bad Catalytic converter or sensors???

Hi,

I'm having issues with my 2003 Toyota Rav4, 125,000 miles.

2 weeks ago my car was driving weird, chugging while driving and my CEL was flashing. I stopped at AutoZone to have them check the codes and got :

P0300 Random/Multiple Cylinder Misfire Detected
P0301 Cylinder 1 misfire
P0303 Cylinder 4 misfire

Because it was a Sunday and my mechanic was closed I stupidly went to Tires Plus, where they said I needed new spark plugs, charged me $260 for that and said that didn't fix the problem and that now it was showing a misfire on Cylinder 2 and they wanted to replace my ignition coil to the tune of $350. So I left there and took the car in the next day to my mechanic. He said it was a bad ignition coil on Cylinder 2 and fixed that for me.

Now 2 weeks after that my CEL is on again, not flashing just steady light on. The car appears to be running fine. I went again to AutoZone to have them check the codes and now I have :

P0420 Catalyst System efficiency below threshold Bank 1
P0430 Catalyst System efficiency below threshold Bank 2


Now I'm wondering what to do next.

Was the ignition coil an indicator of a problem with my catalytic converter or 02 sensors?
or
Did the bad ignition coil cause an issue with my catalytic converter or 02 sensors?

I'm just not sure what route to go as these repairs are going to cost me a lot of money and right now with the car seems to be running fine.

Any suggestion or tips would greatly be appreciated!!

Misty

Sometimes you can weed out problems by staying on schedule.
We have seen bad Air filters, fuel filters, and dirty throttle bodies causing random misfires.

P0420(bank 1) + P0430(bank 2) Low catalyst
9X's out of 10, it's a bad cat!

Have a local muffler shop do a free inspection on both cat's, if the
cats are bad, consider OEM from http://www.catalyticconverterwarehouse.com ,and
have the local muffler shop do the install.