Electrical problems

I have a 87 riviera that I just purchased...It idles rough, and when I get up to 45-55 it kind of stalls out or knocks...the computer displays an electronic engine control problem, my horn and my cruise also do not work...I dont know if that has anything to do with it, but I am mainly concerned about the engine running bad. It would be greatly appreciated if someone could lead me in the right direction about this problem! Thank you!