Car has a very hard time starting when it's wet outside

2002 VW Jetta
My car sputters only upon starting when it's raining or has been very damp outside. I had the wires and plugs replaced about two yrs ago. That helped a lot, but did not solve the problem 100% at the time. Now it's back to sputtering 100% of the time, but ONLY upon starting the car when it's wet outside....?? Once the car runs for a while, the problem stops. Help! Thanks in advance for any advice!!!