2001 Kia Optima LX Stutters and shakes in the rain

Hello,

I have a 2001 Kia Optima. It has 127,000 miles on it. I had noticed a couple
of years ago that when it rains, the car stutters a little while driving. I
brought it in to my mechanic and they were not able to recreate the
stuttering and there were no codes displaying when they scanned so they
said to wait and see if it continued. The stuttering continued every once in a
while, usually only in the first 5 minutes of driving while it was wet. I bring it
in for maintenance pretty often and there was evidence that there was a
problem, at least one my mechanic could see.

A couple of days ago, I was driving up a hill, like I do every day and the car
stuttered and then turned off. It started immediately afterwards but seemed
to run a little "weak" like it wasn't at full power. I tested it again that night
and it seemed fine. It rained again today and I started the car and it
immediately started stuttering. I put the car in drive and it got worse and
then the check engine light came on. I turned it off because the stuttering
did not subside, and it shook worse than it ever had before.

I don't plan on using it again until I can get it checked out, but I was hoping
someone out there might have an idea about what's going on and how
costly it would be to fix. Any information would be very much appreciated!