chk the heater a/c core its not draining water ouyt of the car thats why its ending up in the floorboard.take the cover off the core,clean it,and make sure the drain is working.

Have the heater core checked.

Actually my '04 grand prix is going through the same problem and is a rain related problem... I've been doing research on the subject and this is all I've been able to find... I'm not saying this is necessarily your problem (as I'm not even sure these are the reasons to mine), but is worth checking. NOTE: None of the following are my comments but stuff I've been taking from different forums and glogs all over the net... I have a 2004 with the same problem. There was a technical service bulletin by gm in april of 2005 regarding the issue. The problem is that as water runs down the windshield on the passenger side of the car it runs into the air box. You can find this by this: put your wipers in the upright position, Open the hood. Remove the plastic wiper fluid hose off the clips. remove the rubber gasket hood seal. there is a plastic cowling that covers the lower passenger side of the windshield. this is removed when you change the air filter for the passenger compartment. the trim screws are 2 piece clips. pull out the center (heads looks like a nail, and then pull out the outer section. There should be a 2 foot section of rubber gasket that is on the sheetmetal that the windshield rests on. This is supposed to deflect the water. Mine had fallen off, letting water run right into the fan box. GM sells a new colwing for this that replaces the gasket, and stops the water from hitting the airbox. It is not covered under warranty, but it's less than $4.00. (yes, a gm part for less than 4 bucks). This is easy to replace and can be done in 5 minutes. ________________________________________________________________ Just so you know.....I got my leak fixed today for $6.34. They didn't have the new cowling, but used a couple of cut up plastic anti-freeze jugs that they glued together and put in a new rubber gasket over the top. The water specialist said that a guy from Detroit had showed him the trick. As you said, my rubber gasket had totally fallen off! ________________________________________________________________ Water leak: Water may leak from the A-pillar (between windshield and door) due to a seam that was not properly sealed or onto the floor from the fresh air intake grille (2005) or the water deflector under the cowl needs to be replaced with an improved component. (2004-05) ________________________________________________________________ # TSB #030857006 -- WATER LEAK ON FRONT PASSENGER FLOOR. *TT (NHTSA ID #10005156, MARCH 01 2004)

Did you happen to fix the leaking problem with the grand prix? If you did... I was just wondering if you went to a dealer to get the partor where you did. And if it was a cowling that needed to be replaced or was it something else. Because I have the same issue, but im having some trouble finding a cowling if that's what i need to fix it, and i dont want to take it in to get fixed and pay more than i have to

This is straight from GM: ----------------------------- Date: February 25, 2005 TECHNICAL Subject: Water Leak On Front Passenger Floor (Install Water Deflector) Models: 2005 Buick LaCrosse, Allure (Canada Only) 2004-2005 Pontiac Grand Prix Supercede: This bulletin is being revised to update the models, model years and Correction information. Please discard Corporate Bulletin Number 03-08-57-006A (Section 08 - Body And Accessories) Condition Some customers may comment on water leaking onto the front passenger carpet. Cause Water may be getting past the rubber water deflector located under the air inlet grille panel. During diagnosis, the technician may note that the passenger compartment air filter is wet. Correction Install the new plenum water deflector. Follow the procedure below: 1. Position the windshield wipers in the up position. 2. Open the hood. 3. Remove the hood seal. 4. Remove the washer hose from the right air inlet grille panel. 5. Remove the push pin that retains the air inlet grille panel. 6. Remove the air inlet grille panel. Important: If Corporate Bulletin Number 03-08-57-006A was performed, it will be necessary to remove the strip of foam that was installed on the front edge of the cowl. 7. Discard the rubber water deflector. 8. Install the new designed plenum water deflector. 9. Install the air inlet grille panel. 10. Install the push pins. 11. Install the washer hose. 12. Install the hood seal. 13. Close the hood. 14. Return the windshield wipers to the park position. Parts Information Parts are expected to be available from GMSPO on 3/2/05. --------------------- The replacement part can be ordered from any GM dealership for ~$5.00 When you call just reference the TSB # 030857006

You can also buy a water deflector online at http://www.gmpartsclub.com and install it yourself. The real question is how do you get that stinky water smell out of your car? http://www.chevyclub.org