It is a bolt with a nut threaded on it. Mounted on the rear of the IP, below the shut off valve.
Loosen the lock nut and turn it in until the idle shake improves. If you turn in too far you will find out in a hurry, you will lose most of the power. If memory serves, you should turn it in until the idles smooths, then turn it back out a 1/4 turn? Maybe someone here recalls the exact instructions. If it is left in too far you will lose power and may not be able to back it out of the driveway.
Try to see the color of the pin. If it is brass color, then it is the replacement part, if aluminum silver, itis the earlier old part that will need replacement, not sure which year the change on that was made, your car may have had it to start with. You can get an idea of how worn the damper pin is by removing it. There is a spring loaded pin on the end. That should have a little spring action left, when they get worn the spring action is not there.