'Launching' D3 4.2tdi
 

Something that's puzzled me when I'm driving to work , waiting to come out of a junction/roundabout is how the power cuts on the D3 4.2tdi when holding the brake pedal and building the revs as you would use a clutch on a manual ready to move, (I know this isn't its's intended purpose) the D3 A8 3.0tdi I was able to build a decent amount of revs to launch the A8 however the D3 4.2tdi does seem to want to play

This guy in the video seems top have it sussed, do you reckon he has it held in P build revs and drops into S or am I missing a trick?

https://www.youtube.com/watch?v=MuUMeNzG60M&t=1s

Switch off ESP?

Will be giving this a try later ainarssems thanks,
so frustrating when your trying to get out of a junction and the bite isn't there

Been disabling the esp temporarily whilst getting out of junctions makes such a difference, prior I was getting a 1 second lag, with esp off just takes off +++

I'm glad to hear it helps. Was not sure if it will help but on my A6 C5 TDI if I keep the accelerator down and press the brake it cuts engine power by probably 80% after like 0.5s and if I release brake it takes at least a second before power comes back on, if ESP is off it still does it a little bit but much less noticeable. So that was my reasoning to try it out.

If you disconnected power from ABS/ESP (pulling the fuse or splicing in extra switch) results might be even a bit more better.

I know it's a D3 not a D2, but a problem I (and others here) have with some of our D2s is serious lack of power, accelerating very gently and holding gear changes back. Typically after stopping at a junction (sound familiar?).
This is caused by a very tiny maladjustment of the brake pedal switch which actually has two switches internally; I wouldn't be surprised if the D3 was very similar.

One switch basically operates the brake lights, the other informs the ECUs that the brake pedal is depressed. There is a tiny bit of movement between the two actuating and it is possible to release the brake pedal, removing brake pressure and turning off the brake lights yet still telling the ECU the pedal is being pressed.

It's possible to see this happening very easily by monitoring the relevant channels with VCDS and gently operating the brake pedal. It can be even more obvious with the engine off as there's no servo to magnify foot pressure.
On my S8 this would typically occur after a gentle stop, with the brake pedal only depressed very slightly and released softly. After a heavy braking it would spring fully back and both switches would change effectively together.

The D2 solution is to adjust the brake pedal switch by screwing it in the appropriate direction. Bit of a swine to get at but do-able.

I know many later Audis (and other cars) have "set once" brake/clutch pedal switches with a very specific installation procedure so that may not be an option on a D3, but VCDS could still be used to check how sensitive they were and if they ever "stuck".

It may be the case but I think it's more to do with ESP seeing brake on and sending torque reduction request to ECU, it's not a rally car so it does not expect brake and accelerator to be pressed at the same time and then the D3 tech is not that recent so it takes a bit of time for ESP to see brake released and to cancel/modify torque reduction request to ECU. My D2 S8 does not have ESP so does not experience any of this, ECU only get torque reduction request from TCU when switching gears.

Yes, don't want to digress, but it was just a thought....

Incidentally my (late) PF S8 did have ESP, as does my current FL one, and the ESP reacts EXTREMELY quickly in all aspects.

ESP in my A6 C5 and an S4 B6 Cabrio is quick to cut the torque or to put brakes/ABS/ EDL on, but very slow to turn the power back on, same on couple of friends A6 C6. Can they all have faulty/misaligned brake switch? Sure. Wee need more data from more members. What happens if you go full throttle, hit the brake without releasing throttle, then release brake? How long does it take for power to come back on?

After a few weeks of turning the esp off weather permitting, turning it off definatley give power to the wheels when getting out at a fast junction/roundabout. HP I had the D3 3.0tdi as well as the D3 4.2tdi, kickdowns in both have been disappointing usually not dropping down to the best gear imediately i.e instead of 5 to 3 it will do 5,4,3, I love the acceration of the 4.2tdi from standstill but when your doing 50 and press the loud pedal dowm its a bit disappointing waiting for the drop, i sometime drop one prior with the paddles before going for the kickdown