My 2006 Chevy Silverado 1500 with 4.3L engine has an issue. When it rains significantly, the idle will rev high, then low then high, etc. In addition, when driving, the truck will suddenly dump to a lower gear and the rpms shoot up. It is difficult to drive when this is happening, but it will will resolve after engine is hot (dry?).
My car has 78200 miles.
My car has an automatic transmission.
If you are having random problems throughout the vehicle when it is raining then you most likely have various electrical connectors not keeping out the water and wire connections are shorting causing the erratic issues. You will need to go to each connector that is prone to get wet and goes to the areas having problems and disconnect connector and check for corrosion and then add a dielectric lube to the pins and seal very light and reconnect the connectors. Repeat process until the problem is resolved.