We had a really heavy rain a few days ago. When I went to work the next morning, my check engine light started flashing after driving about a quarter of a mile and when stopped it will rough idle. This has happened before after a very heavy rain, but not every time it rains heavily. We've tried SeaFoam and another water/gas separator (Startron), but neither has helped. Has anyone else every had this problem? My Xterra is a 2001.