Audi A8 2.8 running issue
 

Hi all,

Have had my A8 since May, and in that time have covered 2340 trouble free miles.
That ended today however: the car started well enough and I drove it a couple of miles. I went to pull away from some traffic lights, and the engine stalled. So I put it in neutral, restarted it and it crept, but was unresponsive to throttle inputs. I pulled up to the side of the road and turned the engine off and restarted it. The EML, ABS and EPC lights were on. Also idel was erratic, jumping between 800 and 1200 rpm. The throttle would let the engine gently rev to 2k, but not past - this was only in neutral, in gear it was idle only.
Anyway, I managed to limp home at 10 mph using creep, I had to stop a few times, and when putting in D, it would do so with a bang.
Pulled in my drive, turned it off, turned it on again, and all the dash lights were out, and idled and revved fine! Took for a very quick test drive and it was faultless - moved in to D smoothly.

I know it needs diagnosing; but is anyone familiar with this? Very annoyed as I was planning on going to Europe this week; am happy that it decided to happen now though..

I would check for possible water ingress into the electronics box area (as I call it) under the bonnet. It's up on the right-hand passenger's side next to the firewall and has an easily-removable cover. This may be different on a 2.8 to the 4.2 though that I have. On my car, the ABS box was I think the lowest one, and then my gearbox TCU sits above it. Bearing in mind the recent rainy weather, I suspect that this area might be full of water. It's certainly worth checking.

Hi, yes good shout. I did suspect the rain might have had something to do with it.
I did just look under the cover and it looks dry. I'd like to replace these seal though, just to ensure it stays watertight.
I'll have to get it plugged in.

I'd also check your battery and alternator condition and check that the battery terminals are making good contact.

Will do. Where is the battery located on these, is it under the rear seat?

In the boot, right hand side recess. Should be a cover that just lifts off to reveal the battery. It's quite a tight fit so it's a bit of a faff to get the battery in and out.

Found a photo of the compartment: https://i.imgur.com/ghwxtx5.jpg

Lovely, thanks!!

So drove the car back from London to Bmth last week, everything was fine until the last 5 miles when travelling at 70mph the fault happened again. I put it in neutral turned the car off and on and it was fine - has been ever since.
Took it for diagnostics to a friend who's a VAG specialist, and several faults were logged; all to do with the throttle body, oh and a lambda sensor looked borked.
It's going back tomorrow as they noticed some corrosion on the electrical connections (but the engine bay was too hot to look in to further). So hopefully something conclusive comes back; fingers crossed it's not the throttle body as they're big bucks aren't they :-(

Oh and the cruise control switch was flagged as broken- makes sense as cruise control doesn't work - do I just need a new stalk?

Check out the site sponsors on eBay (a8parts). They have several starting from £28 if you want to go secondhand. If you want to purchase new, give them a call on 01642 783537, as they can order them in.

They might even have the cruise control stalk.

Cruise control has two fundamentally different versions, which depends on the age of your car. As I think is flagged prominently on the forum, it helps if you supply more details of your car as answers do depend on precise vintage, trims, etc.

Ah ok makes sense:
W reg (2000) 2.8 FWD. Not a sport although has 18" sport wheels

2000 should be the "drive by wire" throttle where cruise control is just a bit of software in the ECU. Earlier versions actually had a separate box in the engine bay ECU box and that really could go wrong.

As such, with DBW, the switches on the stalk talk directly to the engine ECU and are pretty simple.
They often get gunged up, spraying with contact cleaner and energetically exercising them can often bring them back to life.
Unless of course they really are broken, but all that VCDS (or any other diagnostic) can tell you is whether it sees the switches operate, not that they are "broken" so this is always worth a try.

Do any of the cruise control functions work ever? Mine didn't when I got the car and it was the end button that wouldn't "set" a speed, so it never worked until I cleaned and "exercised" it. ;)

That's interesting, I'll have a play with the set button. Thank you!!
The previous owner mentioned that the 'set' button worked, but you could increase the speed. None of the cruise control has worked since I've owned it, which is since May only. Best car I've ever had for motorway duties.

Mine's still not great on increasing speed (or resuming), sometimes it just disengages.
So I'm more in the habit of increasing with my right foot (which is actually easier than that horrid little slider anyway) and pressing set again.

I think my slider switch is the least reliable bit so I just leave it permanently in the "on" position. Beating the hell out of the end button got mine working reasonably reliably in the end and you can live without the rest.

The garage have stated that the faults are from the throttle body, so a new one is being fitted. £350 for a new genuine Bosch item. The main dealer wanted 900 quid!!!

I don't know if a logged throttle body fault would inhibit cruise control, it just might, so try it again after the repair.

TB replaced, seems to drive well and idle better with a/c on; but that might be placebo.

I'll have a go with the cruise control later.

One other thing: with regards to the plastic box that sits in the bulkhead on the passenger side, it cotains the abs and tc ecus, os it possible to purchase a new seal to prevent water ingress? Or should i just silicone seal it?

I had a lot of similar trouble some years ago. The TB was replaced and all seemed well - until it rained heavily again (I was in Scotland at the time, so didn’t have to wait long! :) ) and the strange symptoms restarted. In the end, the garage took that plastic box apart and discovered signs of serious water ingress. IIRC, the seal was available as a new part, but it may have come complete with the lid.

Unfortunately you can't buy the seal by itself, as it comes as part of the cover. The part number for the cover is 4D2937128F and cost around £50... if you can find one in the UK. Failing that, you can still get them online from either of these two sites:

E-ACCA.COM @ 44.99 Euro

carparts-pros @ 53.30 Euro

And if you don't want to go down that route, there are a few secondhand on eBay around the £20 mark, although you'll have no idea about the state of the seal.

Hopefully it's not unlike the seal around the air intake and that you can easily buy a roll of suitable adhesive foam strip. ;)

Thanks above for the part number to the seal and cover. 50 quid is small fry compared to fried electronics :-)

Have had a productive day with the A8:

Replaced all the clips on the driver's door after the previous monkey that removed the door card broke them all. Also clipped in the central locking button so that works now.

Fixed the driver's headrest after following a vid on youtube.

Bashed my tip so much that cruise control works!

Oh and bought some genuine pollen filters (x2) from Deutscheparts on Ebay for 15 quid....far cheaper than any other on the maket.

Well done that man! +++