1997 Chevy Astro Van Help????

I own a Astro Van with 77,777 miles on it and when there is just a little moisture in the air or a light dusting of snow, it starts to act up. It acts as if the engine is missing or the transmission is slipping. When it warms up it all quits. When it does act up the Service Engine Soon light comes on. And then goes out when it starts to run right again. When I have it checked all the codes say is it is missing on one or more cylinders. It is very confusing to me, it only happens when it is cold and moist outside. Does anyone out there have the same problem or have had the same problem. What did you do to correct it? Please let me know, thank you