Please i need to know whats wrong

ok my 93 camaro just started doing this the other week. what happens is when i crank my car it idles at 500 rpm(usually ran about 1000) when it gets operating temperature it starts idling rough and eventually the engine stalls out. ive took it to a mechanic and he blocked off the egr valve. well it still does it. went to autozone and they told me that i may need a new idle air control, so i bought one put it on and still does the same thing. ive tried doing a radiator flush and still nothing. tried putting new plugs and wires on it and still nothing. ive tried putting octane booster and fuel cleaner in the tank thinking it may be the gas but still does it. put the highest grade gas in it, dont work. i dont have a service engine light on or anything. when im going down the road if i come to a stop and dont keep the rpm at 1000 or above the engine will stall. ive been told that it may be the fuel pump but wouldnt that cause it to not start at all? the engine runs fine when going down the road but when sitting still it idles rough and stalls out. if anyone can help i would greatly appreciate it. thanks in advance to all who reply.

Get the idle adjusted via a handheld programmer or tuner of some sort. Cars today are being increasingly computerized, so you may have to do it through the ECU/PCM.