Check Engine Light

Hello All...... just wondering if anyone has an idea why my check engine light comes on (and car idles roughly) whenever it is wet outside? Thanks.

My 91 Cavalier does the same thing. She runs smooth with the engine light on but when the light goes out she runs rough and stalls.
Problem is the same with starting. I have to crank her a few times untill the light comes on and it will start. Driving on a flat road cruising without excelerating or decellerating the light also goes off. touch the gas or breaks and the light is back on. Need help on this one too????????

Also have water on the front carpets. Water comes in even when the car stands still in the rain. Windshield is not leaking and all drain plugs are open. AC Heater rad inside is not leaking because the coolant level stays ok. Leak must be from the Heater fan where it joins the top of the firewall under the windshield wiper cover.

sounds like your heater core is plugged, try reverse flushing your cooling system and installing dex-cool or equivalent

Look at your coils remove the plug wires and see if there is crud in there. also take a small plastic spray bottle and with the engine running mist the ign system with water , ign wires , plugs , coils and look for any arcing/sparking and replace anything that does spark