97 blazer MAS problem

1997 blazer 4.3 when it starts the idle is high when I unplug the MAS it then idle right, it is not showing a code for this using a snap on scanner. This truck was purchased by my son from a guy who said it just stopped running that guy put in a new fuel pump still did not start right. he got pissd sold to my son cheap and we put a few things on it before replacing the fuel injectors now it starts fine but the idle is high and then get rough until I unplug the MAS before I buy a new IAC as a guess thought I would try here to see if anyone has had this problwm before.

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