Muck and drains and things

[HPsauce]

Today, as it was dry and a bit breezy I decided to investigate around the ECU box.
The initial thinking was that, given my blocked scuttle drains a while back, some water might have got into the ECU's and cause my other problems of lack of power and poor starting. In the event the box seemed dry inside.

As you probably know there are a collection of large Philips-head bolts holding down a perforated cover plate and the actual ECU cover in an odd mix-and-match arrangement.

The odd-shaped ventilated cover plate is under the passenger side cabin air filter and once I had it off I discovered all sorts of damp crud in the various recesses there. Obviously tree/plant debris from wherever a previous owner kept it.
There was also a fair bit of water between the ECU box and the wing, not deep but not draining completely.
And there was a funny little box with a few wires to it, clipped to the front of the ECU box under the ventilated cover plate, again covered in damp crap. My PF S8 didn't have that

So I cleared away the crud and rummaged around in the wheel arch to check the small drain there.
The drain didn't seem blocked but only a trickle came through, so I reckoned there was probably a build-up of more crud around the top of it - under/behind the ECU box, which largely seemed to be sitting on a bed of damp pine needles and the like.

I pulled the drain out completely and cleaned it, but it wasn't really blocked. But I then gently poured warm water into the wet area and poked up into the hole from below. A fair bit of crud came through and the area drained well, so I flushed it carefully a few more times.

To be continued...............

[HPsauce]

.....continued
The drain went back in OK with a bit of force and wiggling and tested again all seemed to be draining properly.
And while I was at it I checked the scuttle drains; they were clearing fine - any water poured in there came out very quickly under the car.

The area under the perforated cover is where some of the air is drawn into cabin, so all the damp mess there was possibly adding to the occasional condensation I see on the front screen.

With the ECU cover finally off after all the waterworks I checked around and all seemed OK, though there was a tiny bit of corrosion visible on a bolt head inside the box.
I gave it a few minutes blast with a hairdryer anyway and VERY carefully cleaned all the damp debris away from the rather inaccessible rear edge.

I think that rear edge is really a bit of a design flaw as the cover just sort of slides in under 3 big lugs and is directly under the wipers where loads of water falls off the windscreen; the other 3 sides are more firmly held with screws.

Carefully cleaned around the lid, made sure the seal was sitting correctly and put it back, initially just using the few screws that don't also hold the perforated cover.
The funny little box on wires I noted the part number of - as 4D0 907 659 - and googled it with no satisfactory answer.
Anyway, I cleaned it up and put it back then refitted the perforated cover and screwed everything back tight.

No change to the starting behaviour, but at least I know all is clean and dry in that area.

A bit more googling and I eventually found this, which was the little box, the air quality sensor in a logical place.
Maybe I misread the part number slightly: http://www.europarts4sale.com/servle...-dsh-03/Detail

And finally I did a VCDS scan and (apart from a warning about the engine coolant temperature sensor) had this new error on the HVAC controller:
1 Fault Found: 01592 - Air Quality Sensor (G238) 57-10 - Electric Circuit Failure - Intermittent

That's almost certainly down to the damp crud! I have no idea how it got there though.

Overall, the lesson is - get those covers off and clear out all the drains and accumulated rubbish.

[Adrian E]

If you disconnected the sensor that'll throw a fault code just because it can't see it

Sounds like you've covered most of the bases now for water getting in - I know the previous owner of my car had a new ECU lid fitted for about £30 and unblocking plenum drains was an hour's labour so depends how confident you are on how free flowing they are now?

[HPsauce]

Apart from the boot lid I thought I'd done it all already, but the occasional bit of condensation on the windscreen when parked was a mystery, until now.
Quite how so much wet crud collected under the ventilation covers (I'd already cleared the driver side as it just clips into place) I really can't think.

And no, I didn't actually unplug the air quality sensor, but it was pretty mucky so got some robust treatment. I do run with that automatic system enabled but if it fails it's hardly a major problem.

Plenum drains are excellent now, as air the aircon ones. I've still got the transmission tunnel side panels off and will give the orange drains a final check before I put them back sometime soon.