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Hey all. Just to followup. I don't like leaving my threads open-ended... but I forgot to close this one out. The problem was actually the very first thing I thought it was. Mechanical timing was off.
I redid that vacuum test in a couple different locations, including off of the brake booster hose inlet. The vacuum gage needle didn't do that shaking thing again. I think it was shaking because I had been taking the reading from right behind the throttle body. Maybe the throttle body was doing some pulse width modulation that was causing the needle to shake.
The problem was two-fold: the durametric said that my cam deviation was damn near perfect, but somehow I'm 99% positive it was off. Also, the car has an underdrive pulley, so it was hard to set mechanical timing.
I honestly did mechanical timing like 4 times in the beginning of this problem to get the two banks within half a degree per durametric. Over a year later i tried again. I moved cam timing for bank 2 over 2 degrees in one direction. I saw the misfire problem get worse, but in the exact same symptoms, just worse. So i moved it 4 degrees in the other direction and then misfires completely stopped. The whole time, the cam deviation values on the durametric didn't change. So it says it here on other threads in this very forum, but if you have an underdrive pulley and need to set mechanical timing.... good luck. Maybe there's a better way to set the mechanical timing than guess and check.
Hopefully someone else finds this info useful.
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