Hard starting and runs rough on humid days

HI,
I have a 1990 chevy lumina euro 3.1.As stated in the post title humid days are the only problem.In the good old days I would says distributor and cap but since this car doesn't have it am I going the right direction by thinking the coils?I put this motor in last spring.It had apprx. 82,000 on it.Thanks in advance for any input.
Jeff

You Are Right About No Distributor But Their Are Ignition Wires On This Car An Easy Way Is Open You Hood In A Dark Area Or Outside At Night And With A Spray Bottle Water Down The Ignition Wires And Look To See If You Ca Locate Any Sparks You May Have To Rev The Engine Up A Little Like A 2000rpm Thats Were I Would Start Good Luck