1989 Chevy Blazer misfireing

my blazer is sputtering or misfiring at idle and at low speeds.when i give it alot of throttle it dont sputter.the service engine light will come on and off.i change the spark plugs,distributor cap and rotor button,plug wires,egr valve,and idle air control valve.i thought it might of been a vacume leak but i couldnt find one.i also rebuilt the throttle body. please help me find the problem im trying not to spend big money sending it to the shop.

thank you very much