Code 300 muliple cylinder missfire 1998 4.3
 

My Isuzu Hombre suddenly started missing and pinging. I pulled the cap and rotor. They looked good. I haven't pulled the plugs yet but cap, rotor plugs, and wires all were replaced just a few thousand miles ago. I put a code reader on it and got the above code.
It has about 136,000 miles on it.