Having managed to cure (note to self: Check definition of 'cure'...) wet footwell carpets in a 147, I thought I'd put together some bulletpoints on where to look/what to do. This isn't meant to be wholly definitive but at least might be some use to anyone (everyone?) out there in Alfa-land who has a similar problem. So here goes:
1) Wheelarch bung
Behind both front wheelarch liners, at the back of the arch, is a rubber bung about 4" x 2". This is accessible by turning the wheel onto full lock and taking out two screws; one at the lower back edge of the liner, the other between the liner and wing inner panel, roughly at about 2 o'clock as you look at the arch.
This bung leads directly into the sill, so if it isn't properly fitted will
let water inside the car, soaking through the felt underlayer and into the carpets. as the water can pass along the length of the sill it can appear in the front and/or the back footwells.
Remedy: Take the bung out, clean it and the hole well, then refit with a 1/8" bead of silicone around the underside of the bung, in the groove where it fits into the hole.
2) Underbonnet drain
Under the plastic shield, where the wipers are, is a 2" x 1" drain hole. This exits directly into the back edge of the engine bay.
The hole can easily get blocked with leaves and other debris, allowing water to build up from where it can seep in.
Remedy: Remove wipers and the screws holding the shields in place, then pull them away to access the drainage (NB. There is a 'hidden' screw under a round cover at the outer end of the shields). Clean away any debris, etc. then refit the panels & wipers.
3) Door seal
The door seal is a push fit onto the flange around the door aperture. If it isn't properly located then water that runs down the gap between door and windscreen, ie. outside the seal, can seep under it - usually at the front lower end where the seal bends from vertical to horizontal. This will run under the sill trim and into the felt underlayer and carpets.
Remedy: Push the seal firmly onto the flange. If it moves significantly (>1/8") it probably wasn't seated fully. If it still won't seat pull away it off the flange and refit, making sure to keep lengthwise tension on it.
4) Underfloor drains
If you look under your car (147 definitely, not sure about others) you will see a series of curved drainage 'slits' at the rear end of each of the floor channels. These can let water in when it is splashed up (eg. driving through heavy standing water, jet-washing underneath, etc.) and - if the water isn't clean - can 'silt up' and block.
This means any water getting in elsewhere can't get out and that the channels can fill with water. The problem is that these are covered by the black sound-deadening panels that are stuck to the floor.
Remedy: A bit of a drastic - but ultimately satisfying one - is to remove the sound-deadening (it's not very well stuck so most of it will pull away; any remaining bits can be 'helped' with a blast from a hairdryer!). Clean the drains then fit new sound-deadening.
5) Sunroof drains
These are designed to take excess water away so the sunroof doesn't leak. Unfortunately they can block, leading to a build up of water that finds its way down and into the carpets.
Remedy: Locate the drains, make sure they haven't come loose and carefully push a length of flexible wire or smaller tubing through. This should clear any blockages.
6) Aircon drain
Condensate can build up in the aircon if the drain is blocked. This will overspill into the front footwells.
Remedy: Locate the drains and make sure they're free-running.
7) Other associated problem areas
- Bulkhead sound-deadening - this isn't easy to remove (I believe it's a 'dashboard out' job) and can retain water in the felt behind it. Once I'd taken the seat, carpets & underfelt out of the footwells, I eventually came up with a plan that worked...if you nick the flexible hose from a vacuum-cleaner, this fits onto the heater outlet that normally sends air to the underseat outlets. I simply taped the other, open end of the hose under the sound-deadening and ran the heater whenever I was driving
- Heater inlet - the heater takes fresh air from under the passenger-side shield in point 2). If that drain duct is blocked, or if there is particularly heavy rain/wind, water gets in through the inlet and into the heater fan, then drips down. Make sure the drain is clear and perhaps consider a strip of tape over the front 1/2" of the inlet.
NB. Two of the above - Sunroof & aircon drains - didn't affect my 147 so if anyone afflicted by those can add any more details, please do