im not sure if you have an idle control valve,my 89 has one,it controls idlemairmspeed,if its clogged it will cause a popping in the plenum and a hesitation,with eratic idle,mine is located under fuel distributor,its a big silver can looking thing,with 2 black plastic pipes coming out of it,clean it with carb cleaner,then test it,you can leave it off with the pipes off then look inside it,turn key over as to start the car but not fully,the valve should freely open then close.