Cobalt misses in the rain

Cobalt runs fine except when in rain. Engine starts to miss and gets noisy, even knocks a little. Mechanic cannot find anything wrong, no dash light or code. Read on some other forums that I am not the only one with the problem. They haven't solved their issues either. Motor is stock with no mods. Looking for advice. Thinking about starting the car and hitting the front end with water from a hose and see if anything happens. Any suggestions?

Does it make any idffierence if the engine is hot vs. a cold start?

Before Coil-on-plug (COP) style ignition systems, this used to mean that you had a problem in the spark plug wires. Before distributorless ignition, you could include the distributor cap and the coil wire.

Even with COP, you may have an issue with one of the coils arcing over. Try removing the engine cover and spraying water from a window cleaner bottle along each spark plug/coil assembly to see if you can get it to start misfiring.