Boost issues on start up

[Robert Smith]

Hi there I'm new to the s3 8l, I've bought an immaculate 81k full audi history s3 and owned it for roughly 6 months, every time I've used it it's been fantastic, the battery weren't all that great so I've had it changed, and ever since that day its had boost issues on its first run of the day, so basically I could start it up tomorrow and take it out do the usual and get it up to temp, then give it a foot full in say second gear and theres hardly anything other N/A power, now if I pull over switch the car off then turn it back on and pull away it will then kick you up the **** and give you full boost, and then be ok for the rest of the day, park it up get back in it the next day and go through the same issues again, has anyone had this issue and guide me in the right direction, I believe its had a stage 1 map before but unsure what map it is, maybe the battery change has confused the ECU and the map?

 

[badger5]

first port of call is fault code check

 

[Robert Smith]

first port of call is fault code check

It's now in the garage mate hopefully getting plugged in tomorrow, it went in the other day and didn't produce any fault code which baffled them and myself, what baffles me most is the fact that the first start up and drive of the day it's not very quick, but like I say, if I pull up and switch it off then start it again it comes back to full power and goes very well, If the garage cant find it I may have to take it to a tuning company and get the ecu reset and a fresh map installed maybe, it's been a gem of a car right up to the battery change, I'm in norfolk so its finding a decent reputable tuner I can trust to look at it and keep it safe whilst in their hands, I wanted to show the car this year because it's like factory new inside and out, it freaks me out when it's out of my sight lol

 

[danny_dj3]

i had issues with mine when i got it, and off the advice here, first thing i did was got it scanned for probs. this was defo the right thing to do as it pretty much points you in the right direction of where to go.
im still pretty new to the s3's, but thats sounds like a electrical issue, possibly an n75 fault as its the main culprit [afaik] for nasty boost issues alongside vac leaks, the fact you can 'reset' the fault by turning on and off to me anyway suggests something electrical is causing the turbo not to boost = maybe not sending the info to the wastegate to shut. tho i could be wrong

my issue turned out to be a n75 plumbed in the wrong way and an unfound vac leak in the pcv system, which is all sorted now.

good thing to do is post up where you are, and see if anyone local has the vcds and is able to scan the car for you.

edit; posted as i posted

 

[Robert Smith]

i had issues with mine when i got it, and off the advice here, first thing i did was got it scanned for probs. this was defo the right thing to do as it pretty much points you in the right direction of where to go.
im still pretty new to the s3's, but thats sounds like a electrical issue, possibly an n75 fault as its the main culprit [afaik] for nasty boost issues alongside vac leaks, the fact you can 'reset' the fault by turning on and off to me anyway suggests something electrical is causing the turbo not to boost = maybe not sending the info to the wastegate to shut. tho i could be wrong

my issue turned out to be a n75 plumbed in the wrong way and an unfound vac leak in the pcv system, which is all sorted now.

good thing to do is post up where you are, and see if anyone local has the vcds and is able to scan the car for you.

edit; posted as i posted

Thanks Danny, I'm hoping it's not a huge issue, I'm happy spending money but not wanting to change every component to find it's not helped, hopefully I'll get some answers from the garage tomorrow or Saturday when they look at it, who would of thought a battery change would cause such an issue hey

 

[AGB-S3]

Ive just swapped over the alloy after market re-circ valve [ age unknown] for a real oem device , and as if by magic , the odd reductions in torque , at small openings and medium rpm's ' lumpy boost' have vanished, along with, a increase in the mid range power delivery . the chicken like clucking sound on lift off , has also 'vanished .. so far so good

still can hear , what now appears to be the valve working ,in a much reduced way,
but i'm guessing this is normal ..also the hunting , at idle with the air-con on ,
is much smoother ..not gone , but , reduced

It was possible to suck and blow through the top hose connection , on the old valve , so, it must of been back feeding pressure into the system ..from day one may be ... DuH

G,

 

[AGB-S3]

https://www.18t-tuning.co.uk/engine-advice/understanding-n75-valve/

Now the chicken noise makes sense , its a duty cycle , mark-space ratio ., proportional control , pulse width modulation, knock-for-knock etc device
I fitted a new one of these last year, when the ecu had error flag ... should of changed the re-circ at the same time , only £40 c/w post from main agent ..

probably a good place to start

 

[danny_dj3]

with luck, its a simple fix. my n75 didnt show errors even tho it was piped in wrongly, but i did follow advice here, asked a fellow member for a little help and had the car scanned which helped a lot.
from the info you have given, well at least to me, it does sound like theres something not quite right that rectifies once the engine has warmed. possibly damp sensor, loose connection or a failing part.
i'm gonna guess the cars standard bar the remap, and if so, most the stuff is original and that can be an issue too.

but like Bill said, first thing is a defo a scan.

 

[badger5]

17705 is my guess..... and unless on vcds a lot of generic readers wont read this vag code