i have a 94 firebird with obd1 the trick is they need to use the obdII plugin to scan... the people at autozone dont know this because chances are they dont own an f body... go to discount/advanced auto parts. they have an obd 1 and 2 scanner for all cars it should be orange. tell the guy your shit is weird and for him to bring the scanner and all available GM pluggins then just go under your dash and find the one that fits... i just had my car scanned at advanced auto parts on 9th street and 9th ave N in st pete on friday trust me if you walk them thru it they can explain it

if your o2 sensors (or just one) are bad, it will throw a code. when mine went bad it did EXACTLY what yours is doing.. i ignored the problem til it got to the point where the studdering happened all the time... go under your car, wrench the o2 sensors off they will either be black (your running rich) or white (your running lean) chances are if youve owned the car for a while and have not changed these out, there is something wrong with one of them and DO NOT just replace one. always replace both o2 sensors at the same time... a 4 wire bosch o2 sensor is like 50 bucks...

the only other thing it could be (that i can think of right now) is DTC 16 which is an ignition problem thats loss of low resolution pulse signal... basically there is a chip in your opti that measures low and high resolution signals that feed for your tach... either the chip could be bad or somewhere along your ignition/coil setup you have a ground loose (check the bolt that holds your coil ground on.. mine came loose once) but usually if this is the issue your tach will go crazy at certain rpms... and the car could even stall out when you give it gas

check o2 sensor.. and walk the people at discount auto parts thru how your computer works... they will work with you its their job and they have the resources to scan obd1 lt1 computers they just might not know it