Here is a list of old Doom cheat codes you can try. Just type them in during normal game play and see if they work.
iddqd=god mode.
idfa=all weapons & armor & ammo.
idkfa=all weapons & armor & ammo & keys.
idclev=level warp.
idmus=change music.
idclip=walk past walls.
idmypos=where you are in code.
iddt=all map.
iddt x2=shows monsters & items on the map.
idchopper= Chainsaw
idbeholdl= temp light
idbeholds= go bezerk
idbeholdi= temp inviso
idbeholdv= temp invincibilty
idbeholda= full map