I was having a very similar problem. Mine would lock up, the LCD screen would go blank, come back... for no apparent reason. I just started going case-less this past week, and whenever it acts up, I pull off the road and start poking around. I found that the resonator on my iDuino board is lose, so I will be re-touching that with a soldering iron. I stuffed some napkin between it and the chip, and it has worked flawlessly for 3 days straight, (when I would normally get about 1/2 day before). It was not possible to find without poking around at different components when the problem was present, since I had tested all the connections several times and nothing indicated a problem because I was making a connection with the force of my multimeter probes.
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