hmm are the days it does start different in humidity?
i had that same problem (slightly different ) it was the snesors eye in the dist. took it out and replaced it and let it all air dry for aBOUT AN HOUR OR SO THEN REASSEMBNLED WITH OTHER EYE AND RUNDS GREAT
PUT THE EYE THAT DIDNT WORK INTO A DIFFERENT CAR AND IT WORKS FINE JUST HAD TO LET IT DRY SOMEHOW IT GOT MOISTURE AND FOGGED OVER...
sorry for the caps