Check engine light on, need help

[Hollow Man]

I have a '96 Corolla DX 1.6L that has no mods. About a year ago the check engine light came on and I got a code reader from the local Murray's auto parts. It said misfire of cyl 2 & 4. I replaced the plugs,wires,dist cap,rotor & air filter. I still get this every few months and when I pull the spark plugs they are black. It is happening more frequently now and I just clean the plugs and clear the code. I have never had the valves adjusted on the car, would this make a difference or is it just a bad injector? thanks

[martiniracing]

try replacing the O2 sensor(s)

[4AFred]

i also have the check engine light on and it was diagnosed as "Feul metering level (lean)". K have no idea how to correct it.
All i do is remove a connection from the battery for a minute.