Do you have VCDS? Bad running with failed O2 sensors implies a bad MAF, since the O2 sensors normally compensate for it.

If you go to measuring block 99 in VCDS and then switch to Basic Settings it turns the O2 sensors off and runs just on the MAF. If it runs worse, the MAF is likely at fault. If it runs better, the O2 sensors are at fault.

If you don't have VCDS then just unplug both O2 sensors and see how it behaves. If it won't start, put them back and clear the codes then unplug the MAF and see how it behaves then. Obvs ignition off when dis/connecting anything.

no to VCDS
 

MJ - thanks for your reply/advice.

Unfortunately I don't have VCDS or the 'Lite' version either.
My dongle is OBD Eleven / smartphone app

Car was transported back to my local garage on a low-loader and they are currently looking at it. I've sent them details of your suggested troubleshooting skills so will have to wait and see. DS Autowerks is an option if the local garage has no joy. I really appreciate your invaluable knowledge, so thanks.

Erm... slightly embarrassing
 

Update - no fuel!

I appear to have a non-functioning or not 100% reliable fuel sender unit/float thingy. Fuel gauge in my car was on the 3rd segment of 12 so just above the orangey/red warning section but the car was OUT of fuel - how dreadfully embarrassing.

This was after the rather helpful mechanic had checked most things including checking for a working fuel pump. As soon as he heard that working, he correctly suspected no fuel. Slung a tenner of '5 star' in there and she started first time. Suffice to say, Johnny sheepishly turned up at the garage with a bottle of Tanquerray in hand (that's gin, for the uninitiated).

Lesson learned. Tank is now full of fuel which the mechanic suggested may have freed up the float. Let's see what happens. If the fuel gauge is still reading incorrectly, I'll just have to ensure that it's at least a 1/3 full or just go the whole way and fill the tank every time.

That's a fairly common occurrence for D2 owners so no embarrassment in this company ;)

Did the mechanic verify there was no fuel in the tank, or did he simply assume there wasn't based on none getting to the engine? There are a bunch of seals in the pump assembly and if they fail it can suck air at low fuel levels which will obviously cause the engine to stall.

Also, if the pump has been replaced its possible to misalign it when it goes in the tank. That typically causes it to stop at ~20 litres remaining.

Finally, if the pump has been replaced and the return hose not put in to the swirl pot where the pump lives (ie just left loose) it can run out at about 1/4 tank.

Of course it is entirely feasible that one of the two fuel level senders is faulty, but pump problems are the most common cause of this scenario :)

Fuel tank has never been touched in the 8 years I've had the car. I am aware of the issues experienced if the fuel pump has been replaced...

Mine has always suffered from the classic 'park on a road with camber' situation where you park the car and have 50-60 miles range left. Come back to the car later in the evening and I now appear to have 0 miles range lol. This also occurred on my previous A8.

I've taken the fuel level down to almost nothing in the past and previously managed a glorious 18 miles (with 0 miles range indicated) when hunting for a petrol station at 01:00 in and around the Crewkerne area in Somerset. I can only assume with my recent problems that the float got stuck somehow. Anyway, lesson learned. I'll be modifying my behaviour from now on and will keep the tank full.

£10 of five star (as I refer to it) was plonked in the tank and she started first time.

And so it continues
 

Car gave out again last night 5 miles from home, exactly the same symptoms where I suffered from loss of power and then the engine eventually stalled. Whilst waiting for the recovery lorry (thanks to the RAC for thinking logically and sending the lorry instead of a man in a van), I had some time to think about the situation and did some investigation into various forum posts on the tinterweb.

Full tank of fuel in the car. I suspect that it might be the main fuel pump on the horseshoe fuel tank on the A8. Those were the ramblings of a cold and hungry man so please correct me if I'm wrong on that front. The car did start on a few occasions by running lumpy for 5 seconds before dropping to 200-300 rpm and then stalling. Prior to this, there was one slight hesitation of a tenth of a second after starting to drive away from my mate's house and a big loss of power when I 'squirted' it a bit at a slip road.

Words will be had with the garage - that's the second time in a week that I've spent an evening in my car in the freezing cold; not impressed.

That does sound like classic fuel pump failure now, with a full tank. There is only one electric pump, in the right hand side of the tank. There is a second outlet on the electric pump which drives a 'suction jet pump' in the left hand side of the tank to keep the fuel level balanced. The suction jet is basically a venturi powered by fuel flow.

The complete pump assembly from Audi is ~£1K which is daft, but luckily the original VDO pump is available separately here: 405-052-002-001Z for £128.

The extra outlet is the small tube next to the large pickup pipe on the bottom of the pump. This is what makes it unique to the D2:

http://forum.a8parts.co.uk/attachmen...1&d=1548673652

Thanks
 

I seem to learn something new about my car every time you post, MJ. Thanks for these nuggets of info, much appreciated. I'm hoping the car gets fixed today as we've got snow coming and I need to push the ESP button on the dashboard!

Back in the room... but no snow
 

Fuel pump replaced as predicted, MJ. The unit that came out of the car was marked VDO, as was the replacement. It took the garage a while to do, as they'd agreed to pull out my gargantuan sub box which weighs upwards of 60 kilos! Nice and smooth on the way home, and dare I say it - it seemed livelier with a bit of spirited driving as they say. I cannot get over the fact that it's really quite small, and not even as long as a toothbrush. Still, I suppose it's done a sterling job over the last 19 years.

---
Re: my breakdown on Sunday night...
Fair play to the RAC for listening - I didn't want to be waiting for 3 hrs inside a freezing cold car with no engine running and therefore no heating - so I suggested to them about a lowloader. One was sent in due course, so it enabled the RAC to send the man in a van to another customer instead. I love it when people show a bit of common-sense.

Glad you got it fixed - and couldnt agree more about the above.

The AA managed to keep me waiting for 5 hours for a flat bed lorry when I told them it was a crankshaft position sensor that had finally failed on a D3 (and the part was already ordered and at the garage waiting to be fitted but the car refused to start to take it there!)

They firstly insisted on sending out a patrol which took 2 hours total and wasted his time and mine, then proceeded to keep me waiting another 3 hours for a flat bed lorry (they said they were busy with their own lorries).

I eventually lost patience and they finally took the hint and ordered a local flat bed breakdown truck to come out, who said he was only 15 minutes away and could have come out at any time earlier had they had authorised him to come!).

Suffice it to say, I am no longer using the AA and will probably never again!