1988 Pontiac Firebird Engine will not hold idle?

I have a 1988 firebird formula with a 305 TBI motor. I have recently replaced the cruise control actuator and the ignition tumbler (non anti-theft). My car fires up just fine and then struggles to maintain idel at 400-600rpm fluttering, then shortly after dies, I can aslo rev the engine to any rpm above idel and it will fall and die immeadiatly.( Seems like its choking its self out). After alot of troubleshooting I changed the MAP sensor, due to a lack of continunity in the sensor. And I also replaced the Idle Air Control, bacause the old one was slightly damaged (with dirt) so a good idea to change). My car is showing codes 15, 23, 34, 54. The 34 should have beed fixed my the MAP (no mass airflow sensor). And the 23 and 54 both include the Mixing control soleonid (which I cannot locte in the car or in the haynes manuel that im using. The wiring harness checked good for voitage to the sensors. I really dont have alot of money to throw at this problem. ( I aslo know that I need a coolant temp senspr for the fan: Code: 15). Any advice is very helpful, my next step will be to take out and examine my egr valve. Any insite into why the car will not hold idle is greatly appricated.