Why is my car stalling in the rain?

I had an issue with my car dying, following some "clicking madness" under the dashboard. It turned out that my coolant was empty (oops) and after I fixed that it seemed like everything was ok (they flushed the coolant tank and it was leak-free). However, I have noticed that since then when I am driving in the rain my car will start to sputter and die when I have to hit the brake. If I rev the engine it chugs a few times and lurches back into gear but if I can't rev the engine (rush hour traffic anyone?) - it dies. It seems like it is fine in regular weather. I am hoping there is something easy I can do to fix it - anyone have any ideas? Thanks!!! Oh, and it's a 2004 Ford Focus ZX3