Engine shaking, check engine flashing (have error codes)

Maintenance/Repairs
1

1999 Toyota Corolla

Error codes:
P0301
P0304
P0300
P0420

Symptoms:
Car had short touch of the shakes in the morning, parked it for 8 hrs, drove half a mile, and it got the shakes bad and seems like it wants to stall out and the check engine started flashing. After a minute it went back to normal, and then the whole thing happened off and on the last half mile home.

Background:
I was told the catalytic converter was in bad shape last time I took her in so I’m assuming that’s it. Friend of mine suggested driving it hard to burn out impurities in the cat, but I’m worried about damaging the engine. Going to replace the sparks and spark wires (they’re about due anyways), any other info or suggestions would be much appreciated.

2

“I was told the catalytic converter was in bad shape last time I took her in so I’m assuming that’s it.”

You are confusing cause and effect.
Yes, the catalytic converter is undoubtedly now in bad shape, but that is the result of lax maintenance and/or continuing to drive while the engine is misfiring.

Yes, you should go ahead and replace the spark plugs & plug wires in order to (hopefully) fix the engine misfires that the first 3 codes indicate, but at this point you can’t turn back the clock in order to resurrect a catalytic converter that was heavily damaged by the misfires.