I have a '91 Z28 w/ 350. Was checking everything out yesterday and found that the distributor bolt was loose and it could be turned by just touching it, so obviously my timing is jacked up. Got the timing light out, disconnected the wire to set it, no timing mark showing. Turned the dist. and still nothing. So I figured the prev. owner stabbed it 180* off or something. Set it to TDC stabbed the distr. w/ rotor pointing at #1 on the cap, put it back together and try timing again. Still not showing the timing mark. I revved it a few times and the timing mark appeared. WTF? set it turned it off reconn. the wire and started. Used the timing light to see where the mark was with the car controlling it and way off! Idle was messing up. I revved it a couple times and the timing mark moved closer to the range, let idle and was kinda jumping around. WTF do I need to do here?

 

Looks like you need to start over. Put the engine on tdc on the #1 cylinder and then put the distributor back in with the rotor facing the #1 cylinder and go from there. Tighten the hold down just enough so you can turn it and it will stay so you can make adjustments from there. Then once you have the timing set tighten the hold down all the way and you are done. It's not hard at all. If it still jumps around after that then you need a new timing chain.