I am trying to find what the codes are for 1991 Olds Cutlass

Code 34 is for map sensor voltage low, which means the vac is higher than it should be.
The map sensor would need to be checked.

Scan the computer for trouble codes. Use an OBD 1 scanner or code reader. The light having come on means there is a stored code or codes to direct you or a technician to the problem sensor or circuit.

engine quits when you let up on gas pedal

I might be able to help you on this. I will you two options
1.Sounds like your fuel mixture is too lean or breather pipes from inlet manifold are leaking or idle sensor valve faulty.
2. check your clutch sensor. It might be disconnected. this also leads to engine stalling problem

It's the maf/map sensor circuit.
maf--- mass air flow sensor
map--- manifold absolute pressure.--- check the small vaccum hose from the map sensor to the source, could be brittle and leaking air.
Have both the map and maf sensor checked for proper voltage, one or both could be bad. A repair shop shouldn't charge much to do that.

Most likely it's a fuel pump relay. It's on the panel under the hood.

I am having a similar problem, but there is no check engine light. It seems that mine dies at the light or running, if the rpm's drop. I am wondering if the Idle air control valve is bad or possibly the ERG valve?

Code 28 is transmission gear switch circuits, code 44 is a lean exhaust indication

i dont have it but if you register at www.autozone.com you can get it for free and registering is free and they have all kinds of free help and diagrams for you

THE QUAD DRIVER IS BUILT IN THE COMPUTER.I WOULD REPLACE THE COMPUTER THEY ARE NOT EXPENSIVE ON YOU VEHICLE.LOCATED RIGHT FRONT INSIDE KICKPANNEL!