I'm cross posting this here in the A3 section, as while its relating to my A4, the engine and management systems are pretty similar and i'd like to try and maximise exposure. If you simply treat the car as an AGU engined A3 that gives a close comparison to the engine and management system used.
So i'm trying to work out if this issue is just a quirk of a turbocharged car, or something specifically wrong with mine.
I've noticed that there seems to be a delay of approx 1 second, between pressing the throttle and actually getting boost, primarily when coming from a no-boost, cruise or overrun state.
I notice it most when pulling off in 1st gear. I've found a few times for instance that say you pull out onto a roundabout in a normal, unhurried fashion, then notice someone coming round a bit quicker than you'd anticipated, so mash the foot to the floor (still in 1st gear). I find that the car accellerates slowly, much like a 1.0 corsa or something equally crap, then after perhaps a second, BAM the boost comes in hard and your wrenching at the wheel to keep it on track.
I'd at first put it down to the engine simply not doing high enough RPM to spool the turbo, but i've since noticed that the surge comes well over 3k, a point at which you'd expect the turbo to be fully spooled.
In higher gears the symptom is still there but less noticable in that the additional load stops the revs climbing so quickly, so you dont really notice it, unless your looking for it, and you only really notice it if you apply lots of throttle at once.
Upon actually investigating i discovered that the issue is even present on a full throttle run thru second and into 3rd. When i went into third and gave it full throttle again, there was a very noticable delay (again around a second) before the car started accellerating at maximum thrust again. Given it was up around 4.5krpm i'd have expected instantaneous throttle response.
I tried to take some logs, but its hard to log it, because logs are typically made at full throttle from a low RPM. The only bit of the log that really shows what happens is the aforementioned 2nd then into 3rd pull, as if you plot the airflow figures as a graph you can clearly see it take a second or so AFTER full throttle has been applied, to get the flow back up to the point it was on the 2nd gear pull.
I'll try and post my log data and a graph showing the oddness.