My car has trouble starting after it rains...?

My car is a hyundai accent gl 2000 and I have had it for awhile now. It has been having trouble in that after it rains it makes the sounds of starting but it has a violent shake to it- after which I have to shut it off and then restart it and it is fine. Plus, my check engine light is on. it has been to a mechanic a couple of times to see what the issue is but it hasn't been resolved yet. Any ideas?