A weak battery can cause a problem. Swap batteries with another vehicle that has a good battery to see if that solves the problem before buying a new one. As for the timing jumping around that could be a loose timing chain but at 70k miles that's the last thing I would check. My car had a surging idle, missed, died and then wouldn't start. Other times it would just miss and the passenger bank of plugs would appear to be running rich. That's what made me nuts the problem was never constant. If you haven't replaced the cap, rotor, coil, and plug wires they should be checked as well. Hang in there. I know it can be frustrating as all get out. At one point I was so angry I was hoping my engine was toast so I could build the 331 I want for the car just to be done with the problem.