Can driving in a fairly heavy rain cause the SES light to come on? Last night I was driving down the freeway and the engine seemed to lose a little power and the SES light came on. Today it is sunny and warm. No light and it runs fine.

 

Sounds most likely that some water attacked your opti

 

It happens to me when it rains really hard or I go over a big puddle, but I don't get a light. The car stumbles want's to die for about 2 minutes then goes back to normal.

 

in a word YES
damn opti crap
the SES light in my 97 would come on in a carwash

 

Could be the opti getting wet, or it could be a plug wire or something else. If it does it enough, it will set a DTC code.

 

Why guess? Get it scanned. Even though the SES light if off, the code is still stored in the PCM.