Car misfires

MY LT1 (92) has been misfiring for quite a long time now (about 2 years).
At the begining I had a code 43 together with this problem. I changed the fuel filter, the spark plugs, checked the wiring...the problem remained...
Then I had a code 16...So I decided to change the knock sensors. That solved the codes problem (I have no code stored now).
But the car still misfires, and this happens randomly (speed and RPM varies from one occurence to another) and this doesn't happen every time, one day the car may run fine and the day after it can misfire (though it occurs at a random speed it is in the cruising speed range)
Help me solve the problem guys
Thanks








