[crainholio]

Drop the ECM from under the dash, and whack the case w/ your hand while the engine's running. Sounds shadetree, but when they have intermittent failures due to loose solder joints this will usually trigger (or rule out) a problem there.

After that I'd go after a ground problem. I think the sensors share a common ground on the back of one of the cylinder heads, might be loose or corroded.