89 4.3L cut off hard 1 sec after start up

My blazer was "running" ok with the problem of shutting off after comming a stop (red light), but now when i start it, it shuts off hard and rough. The only way to keep it idleing is to apply a little pressure to the gas pedal. these are the parts that have been replaced within 4 months: plugs, wires, map sensor, IAC sensor, timing chain, starter, cleaned egr valve, ignition coil,sending unit, fuel filter, and module. I am starting to think maybe one or more of these parts are faulty... any help is greatly appreciated.