Mikeythrash

Not sure where to start it's been a year of trying to figure this out but my engine light has been on for months codes read that all 6 cylinders are missing.now today my engine light just randomly went off ? It runs very rough but only when I start it at idle.On highway it's smooth coming to a stop or a light the thing just putts and shakes like it's gonna shut off but it has never stalled.I did take out my IAC and cleaned it.is the valve that sticks out supposed to be loose and spin? I feel like I may new a new one.But also was thinking maybe it's a fuel pressure related thing...But again will that cause all 6 cylinders to misfire? I am at a loss for words anyone wanna help me out here .would be great. 96 XJ 100,700 miles