2002 Elantra won't accelerate when engine is cold and humidity is high
 

When humidity is high (80% and above) and the engine is cold, our 2002
Elantra won't accelerate properly. It hesiates for a few seconds and then
all of a sudden it accelerates (usually 15-20 seconds after starting the
engine). This never happens once the engine is warm or when humidity is less
than 80%. Unfortunately the computer doesn't detect a fault. Any idea what
could cause that behaviour?

TIA