1991 Toyota Corolla Engine pinging

Noises problem
1991 Toyota Corolla 4 cyl Front Wheel Drive Automatic

i have a toyota carolla 1991, I have this problem where it pings at 1700-2000rpm, to try fixing this prob, timing belt was changed, distribrutor, was changed, I used seafoam once, in oil, gas and air intake, I used octane booster once, I use injector cleaner everytime I put gas, distrutor timing was checked, and it still pings what can be the prob, am thinking of selling because of this prob