A8 4.2 TDI - Are they normally this slow?

[sutherland]

Having had several A8s I now have a 4.2 TDI, which I find disappointingly slow. According to the claimed figures this car will do 0-60 in 5.7 secs. Mine, however, will do it in 7.0 and cannot get below that.

I can find nothing wrong with the car--no fault codes or obvious problems anywhere. The worst I could say is that the gearchange is a little slow--almost as if it bogs down slightly before changing up on acceleration, but I put this down to a typical kind of diesel experience. It's certainly not as Evo Magazine described it in their review: 'Gearchanges glide through the six-speed Tiptronic automatic with a barely perceptible change in engine note, and without any interruption to the remorseless surge of thrust. And suddenly you've wafted into the 155mph speed limiter...'

Is it just the case that the real world performance of these cars is not as claimed or should I be looking for a problem somewhere?

Any advice or experience would be appreciated.

[RanjS8]

Normally people are saying these are really quick...so I m surprised you are saying it is slow. I would get it put on dyno and see what kind of power it is putting out.....also it might be worth while having a look for any obvious boost leaks.

Finally....I wonder if these have a dpf or if the mileage is low and causing carbon build up?....in short I agree I would be expecting far better from a 4.2tdi.

[PsYcHe]

I do notice a little pause on the gearchange, and whilst I've never times the 0-60, it's definitely quick.

[sutherland]

Thanks for the responses.

The mileage isn't that low and I believe they do have a DPF. I could certainly have a look for obvious leaks, but wouldn't that cause a check engine light?

I'd be interested to know what 0-60 times other owners get in real life. I checked it via OBD on several runs, so I think it's fairly accurate.

[sutherland]

I've had a development with the CEL coming on and the following fault code:

004204 - Throttle Valve 2 P106C - 001 - Stuck or difficult to move - Intermittent

I guess this could be behind my poor performance, but I'm not sure what the solution is. I didn't think the 4.2TDI had the intake manifold problems common to the 4.0 or that they had the throttle body problems common to the 3.0. I'd imagine if the valve was really stuck that I'd know all about it.

Normally sticking such a fault code into Google brings up a whole lot of stuff, but this one only brings up a post in Finnish about from a 4.2 TDI owner with the same problem, which he seemed to think was somehow related to DPF regeneration. There are plenty posts concerning 004203 / P106B, which I assume is the same problem on cars with one intake manifold, so I might work out a solution from that.

[Paul r]

Hi,

My 4.2tdi is pretty quick. It pulls in all gears and it shifts smoothly through the gears.

I had an e60 m5 before the a8 and performance Wise, the a8 doesn't feel that far behind it.

Paul.

[sutherland]

Hi Paul,

It does seem as if my car may be a bit sluggish. My first priority is to sort out the throttle body. I took it off and cleaned it today. It was fairly gungy and I got it moving more easily, but it does not close completely and is stuck about 20-30 degrees open. I'm not sure what could be causing this and I'm reluctant to force it. I may try removing the plastic cover and seeing if there is anything obvious amiss in there--perhaps they used the same feeble plastic gears as they use in the MMI display.

Does anyone know how to do the throttle body adaptation in VCDS? The usual procedures as outlined by Ross-Tech seem to assume only one throttle and the channels they mention are not the same on the 4.2TDi.

Thanks

Philip

[sutherland]

I eventually got my throttle body replaced and a DPF regen, which improved performance and stopped a wailing noise caused by back pressure. However, I still think the performance is not what it should be--at least it's a long way from published figures. I get the following best figures:

0-60: 6.7s
1/4mL 16.1s 99mph

Does anyone else out there have an Torque Scan running on their Android phone? If so, and you've got a 4.2 TDI, I'd be interested to know what figures you get for your car using the realtime information. Perhaps the claimed figures of 5.7 secs are actually miles away from the real world.

[IT]

Mine doesnt hang around either. I'm more used to it now, and once north of 30mph I'm convinced it would give a W12 a run for its money. Its certainly a lot quicker than the 3.0 Tdi, or the 4.2 petrol.

My gearchange in 'Drive' is sluggish to say the least, and round town often feels like its bogged itself down in the lower rev range with the turbos offline, but in sports, or manual, or just at a cruising speed, its very hard for it *not* to be picking up speed rather quickly

For a daily driver, it really does seem to be the engine of choice. Yes, the W12 or V10 will sound/perform nicer - but - using twice the fuel, and thats a staggeringly huge cost for some audio pleasantries and 0-30 elitism...... (Not that a V8 sootchooker sounds that bad tbh)

I know it doesnt help at all, but the 4.2 Tdi in the wifes Q7 feels *even* quicker, although I'm sure its a gear ratio thing, but for a 2 ton+ barge my god that thing shifts. I quiver at the thought of what state the V12 Q7 would leave the tarmac in......

Im Apple, not Andoid, but happy to do some tests on my motor if it helps.....

[sutherland]

Thanks.

Don't go to any trouble with the tests, but if you happen to have a way of measuring performance figures via the OBD port, I'd be interested to know the results.

The car goes fine, so perhaps it doesn't matter, but if my 4.2TDi is 1 sec slower to 60mph than every other car, it would be nice to find out why.