My 1999 Toyota Avalon has a leak that I can't find. When it rains the floor boards on the passenger side are both wet. I have a sun roof so how are the floor boards getting wet and how do I fix it?

There are 2 'weep' holes where tubes come out of the firewall and sometimes they get plugged. Get some compressed air and blow them out.

Also, inside the vehicle, there is a plastic pan that catches all water that might come down from the evaporator or leak from the outside into the interior of the car when the seal is not good between the firewall and the plastic pan that spans from the left to the right of the car under the dash board.

Get some expanding foam in a can and spray it up against the juncture between the firewall and the plastic water pan. This should seal out the problem if done properly.

Over time, the original foam seal goes bad and can actually flake away.

You mentioned the sunroof. Make sure that all the gaskets and that the sunroof does not leak onto the floor. This can be another source of wetness for your vehicle.

Try testing it by spraying water down from a hose to the top of the vehicle, or dumping a bucket of water all at once on the top of the roof. If it leaks, try using silicon sealant to seal any gaps that may exist in the sunroof.

Hope this helps.