I own one, you can adjust it. There are two adjustment screws, one for each jet, but they are hidden behind a seal, you have to drill through a plastic like cap that cover the adjustment screws, email me for more specific details.
Assuming you have a 305 V8 with a Rochester Quadrajet carb. You will have to pull the carb, and tear it apart. The TPS sits in a groove in the front of the carb body. Buy a carb rebuild kit, watch the Youtube videos on rebuilding quadrajets, and do it. I just rebuilt my carb over the weekend. My 83 Caprice now runs great.
choke not working
Yes, exact fit! Just change the ignition key cylinder to retain use of same keys.
In an '83, the chances are that you pull the knobs and unscrew the nuts they cover.
Start at 1 1/2 turns from seat and adjust for best idle 1/4 turn at a time
On my 83 z28 305 it is 700 rpm
check the ammount of gass an air entering you carb that could be why it runs that way all you have to do is adjust the screws on the front of your carb it would be smart to put some carb cleaner in it too
usally about 8 or 10 degrees BTDC will work fine to get it going.
only a 350