I had a similar problem, but my carpet was staying dry, while the pad under it was getting soaked. This also went back to the driver's sider rear floor pan. I found that I had a couple of leaks in the fire wall. I used some 3M Strip Caulk to fix this. Your situation might be different if your carpet is wet, like the other's have said, check the winshiled, and also check the roker drains. If they are clogged, they will seep water into the inside too. Good luck and happy bricking.

Do what Mark says. Moving water, when it is the only thing moving, even in small drops, is hard to miss.

I suggest you lay across the driver's seat so you can see up into the underdash area and the firewall and then have someone hose down the windshield and cowl area with a garden hose. The corner of the windshield is a known problem spot for leaks on older 200 series cars and there are a couple of grommets that go through the firewall that can also leak. Get a flashlight, a buddy, and a garden hose and check it out.

Mark