I have a 2000 Chevy Blazer that will cough and sputter starting when it's humid, yet once dry weather comes in it start beautifully....I'm really confused. Just put in a brand new altenator, so that's not it and the battery is new. Again this only happens on humid days.

 

What helps for me is spray everything with WD40 under the hood, by that I mean the cables, make sure the engine isn't running. It takes the moisture away.

 

Have you done a tune up?

I have heard condensation can get in the distributor cap when it gets old and that can really mess things up.

I had a similar problem before with my truck. Turns out one of the plug wires was split and when it would rain that plug would short out.