I have a 1995 Audi A6, i was wondering why my car wouldnt go out of 2nd Gear and now today it wont start, so i go to thinkin i did see water in the floor boards, and come to find out my Ecu was half submerged and i took it apart and looked in it and its all fried up and corroded! i found me another Ecu for 75 buxs, but i need to know how to stop this leak in the front right pass foot well and in the back floor board! any help would be appreciated, thanks

 

first off I would remove the carpets and hose the car down to see where is coming in, clear the sunroof drains and the scuttle panel under the windshield especially near the pollen filter

 

Check around the car for grime in the corners and other little cracks i've seen water leaks come from leaves and grime build up around the windshield and near the trunk. I would do what dave says and just open all the doors and the trunk and clean out all the crap that gets in there.

 

Far and away, the biggest infiltration point the passenger compartment pollen filter due to clogged drains in the battery compartment. Remove the weatherstripping holding the plastic batter cover in place at the rear of the engine compartment. If there's standing water in there, you've found your culprit (the pollen filter is the low point so if the water builds up, it overslows the filter and enters the passenger compartment). One drain is located under the batter, the other to the right (toward the driver's side). Once you've unclogged the drains, remember to clean debris from this area anually.

The other culprit (less common) is the drain for the sunroof. Do a search on that to figure out how to unclog.

Good luck.