i have found condensation under the rug mats of my 2000 toyota tacoma more so on the passenger side but have found it on the drivers as well when i take the mats out the carpet seems to stay dry ??

 

I had this problem with the drivers side, and there is a rubber gasket back behind the pedals that goes through the firewall to the engine bay. My gasket had gotten a tiny crack in it and water was seeping in which was soaking my carpet/mats and making my 4runner smell terrible. I threw some RTV on it and called it a day, no leaks since and carpet is dry.

As for the passenger side I can't help too much, A/C condensation maybe...?

 

Assuming no coolant smell (would be easy to detect)...

See if your a/c drain tube is blocked, passenger side on the firewall, down by the a/c hoses, a little tube that goes nowhere and should be a small metal elbow though sometimes the elbow is missing. The a/c condensor box is the big black thing under the glove box on the passenger side. Be gentle poking anything in there...