1998 Honda Civic P0302 Trouble Code

Computer problem
1998 Honda Civic 4 cyl Automatic 82000 miles

I have a 1998 Civic LX. A couple of days ago I noticed the car running sluggish and at times it seemed like it would die when idling at a stoplight. Soon after, the CEL came on. The code it showed was P0302. I drove the car to my local mechanic, about 5 miles (10 minutes) away. He reset the CEL and drove the car 8 miles, no code! He inspected the plugs, wires, cap, rotor and all was fine. He thought it could be a one-off drop a water in the fuel injector since it has been extremely wet and snowy here. I drove the car home 5 miles, no light. A day later I started the car and the CEL came on again, again with the same P0302 code. I drove the car for about 10 minutes and reset the code, and just like the day before, no CEL for my ride home. It seems that the misfire is not taking place when it warms up, but what could be the problem when the car is not "warm"?