My 2002 Monte Carlo has had water in the passenger floor twice after heavy rain. The windows were up.
This car could be similar to my 1998 Regal. I had the same problem. If there is a cabin air filter, it could be above the heater/AC blower motor. If so, access is under the hood. Remove the passenger side wiper and then remove the cowling under it. You should see the cabin air filter. There should also be a piece of rubber window gasket (about 12" long) attached to the bottom of the windshield and directly above the cabin air filter. It may be missing or dislodged from the windshield. Push it back into place. This may solve your problem. It solved mine. BTW, while you’re in there, you might want to replace the cabin air filter.
Don’t use a lever to push the wiper arm off the wiper motor! If you rest the lever on the plastic cowling, you will break the windshield underneath it.
And if this is the problem, the water got into your foot well when the blower filled with water. You should pull the blower immediately and dump the water out. Then hope that the bearings stay quiet. If not, you will need to replace the blower motor. Unless the squeal doesn’t bother you.
If you have a sun roof, that is were you want to start looking for your leak. Usually it is a blocked drain. there is a drain at each of the four corners. A little gentle compressed air or some string trimmer line will often clear it out and you can go back to dry feet.
You could also have leaves in the front area where air is drawn in for your heat&a/c. Most cars have an area accessible under the hood at the firewall where your interior air is drawn in which has drains on either end. If those drains get plugged up with leaves or debri, the rain water can back up and spill over through the duct of your a/c and dump water on your carpet…
it is autumn… and leaves do fall in the fall.
do you park under a tree(s) maybe its time to trim the trees! leaves and pine needles are great to clog up the blower intakes, and drains.
Thanks guys… this is my daughter and son-in-law in Portland, and yes they said the pine needles are bad. I think we hit on it with the needles in the air intake.