i have a 2001 Mazda 626 4cyl had a flashing light car was misfiring shaking when at red lights an stop signs changed spark plugs a bad wire still was misfiring got a code about a misfire in cyl 4 bank 1 generic changed the first o2 sensor o2 sensor was warped an corroded ran a lil better still was misfiring a little at stops changed ignition coil still misfiring should i change the wires should i change the other o2 sensors going to go back to the auto store get the code off the check engine light forgot what it was thing it was a 0420 0421 dont remember any ideas

 

Yes, change the wires too. Since one is new they have different resistance now. Wires burn out internally.
P0420 is about insufficient converter efficiency. So you need to think what affects the converters.
Lean or rich air fuel mixture: leaking fuel injectors, leaking fuel pressure regulator, EGR malfunction, vacuum leaks, dirty air filter, dirty MAF sensor and so on.
Because there are so many possible causes I would go from cheap to less cheap. I.E you can clean and re-use the EGR valve. You can clean the throttle body etc.

Since the O2 sensor was warped I think it may have gotten way to hot. Lean mixture burns hot. Look for vacuum leaks.

 

thanks im gonna follow those steps an get back to you when i figure more things out appreciate the reply