Mine did that a couple of times when it was rainning really hard. I wrapped the connectors in saran wrap and covered it with aluminum foil for protection and it hasen't done it again. My conclusion that it was the moisture getting to the connectors somehow and throwing off the signals by increasing the resistence of the wiring due to the water, probably confusing the computer.
It doesn't look real great, but no one is looking under my hood anyway, it's low cost and if it works it works, so far 4 months no problem.
You might ask him if he remembers being in the rain when it happened.
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