r/AudiS4

I’ve been lurking here for months, but I finally pulled the trigger on this B9 S4 and I couldn’t be happier. Coming from a stage 1 GTI, I knew it would be an upgrade, but the way this car puts power down is just on another level. The interior feels like a cockpit compared to what I’m used to, and that exhaust note in dynamic mode puts a smile on my face every single time I hit the gas.

I’m planning on keeping it stock for a few weeks just to get a feel for it, but I’m already looking at some 034Motorsport tunes and maybe a new set of wheels. Any "must-do" first mods or maintenance tips you guys recommend for a new owner? Excited to finally be part of the community!

https://www.autotrader.co.uk/car-details/202603160728484?journey=PROMOTED_LISTING_JOURNEY&sort=relevance&searchId=1c527f2b-518c-4453-b123-aab2d339989d&fuel-type=Petrol&make=Audi&minimum-badge-engine-size=1.4&model=S4&page=1&postcode=DN2+4JQ&price-to=15000&transmission=Automatic&year-from=2015&advertising-location=at_cars&fromsra=&backLinkQueryParams=channel%3Dcars%26flrfc%3D1%26fuel-type%3DPetrol%26make%3DAudi%26minimum-badge-engine-size%3D1.4%26model%3DS4%26postcode%3DDN2%25204JQ%26price-to%3D15000%26sort%3Drelevance%26transmission%3DAutomatic%26year-from%3D2015&calc-deposit=1549&calc-term=48&calc-mileage=10000&calc-selected-product=HP

-B8.5

https://www.autotrader.co.uk/car-details/202602230136590?sort=relevance&twcs=true&searchId=903428cf-fc27-4168-af85-64cc7a49de5e&fuel-type=Petrol&make=Audi&minimum-badge-engine-size=1.4&model=S4&page=1&postcode=DN2+4JQ&price-to=20000&transmission=Automatic&year-from=2017&advertising-location=at_cars&fromsra=&backLinkQueryParams=channel%3Dcars%26flrfc%3D1%26fuel-type%3DPetrol%26make%3DAudi%26minimum-badge-engine-size%3D1.4%26model%3DS4%26postcode%3DDN2%25204JQ%26price-to%3D20000%26sort%3Drelevance%26transmission%3DAutomatic%26year-from%3D2017&calc-deposit=1949&calc-term=48&calc-mileage=10000&calc-selected-product=HP

-B9

https://www.autotrader.co.uk/car-details/202603040391548?sort=relevance&twcs=true&searchId=dfd96b60-8ee4-4758-9795-593944e9a4ae&fuel-type=Petrol&make=Audi&minimum-badge-engine-size=1.4&model=S4&page=2&postcode=DN2+4JQ&price-to=20000&transmission=Automatic&year-from=2017&advertising-location=at_cars&fromsra=&backLinkQueryParams=channel%3Dcars%26flrfc%3D1%26fuel-type%3DPetrol%26make%3DAudi%26minimum-badge-engine-size%3D1.4%26model%3DS4%26postcode%3DDN2%25204JQ%26price-to%3D20000%26sort%3Drelevance%26transmission%3DAutomatic%26year-from%3D2017%26page%3D2&calc-deposit=1830&calc-term=48&calc-mileage=10000&calc-selected-product=HP

- B9

Hello everyone!

I've been having issues with the classic rattle noise coming from the exhaust, but then stops once the valves are opened.

I was thinking about unplugging them to keep them open, but have a few questions.

1. Since the valves automatically close when turning the car off, how do I open the valve before unplugging it?

2. Is there a valve box on both mufflers?

Thanks in advance!!

2018 Audi S4 Bad Turbo? 96k miles. No boost/spool/power

Hello! I have a 2018 audi s4 with 96000 miles on it now, stage 2 034, for around 10-15k miles now. My turbo just recently stopped giving any boost, it doesn't spool up at all, which you can usually hear very clearly because of my 034 intake. It randomly stopped giving boost and my car has barely any power.

The only code I have is "P029900" for Turbocharger Under boost. I have never had this issue before and don't know what is causing it. I haven' touched anything under the engine for 10k+ miles other than a brand new pcv breather hose that has no leaks. My turbo inlet also has no leaks and there are no new sounds that are being made.

Does anyone know the cause of this and what might be the problem with my turbo? Everything I've seen/read online lead me to think it's the wastegate being stuck closed, which means I'd probably need a new turbo or the wastegate actuator not working.

Has anyone dealt with this issue before and what should I do? I can try to get a video tomorrow with every sound the engines making and the no boost/spool. Thank you

About 4 weeks ago I had a resonator delete done at a shop. O2 codes appeared day 1, car drove fine for 2 weeks, then progressively got worse. Now it idles rough when warm (fine cold), has hot restart issues where it jerks and stalls after driving, and there’s a rich fuel/metallic smell from the exhaust. Drives completely fine under load though, pulls hard, no hesitation.

OBDeleven shows both banks running severely rich — STFT maxed at -37.5% both sides, LTFT Bank 1 at -9.4% but Bank 2 at -59.4%. Downstream O2s are pegged at 0.85-0.96V confirming real rich combustion. Fuel pressure is 34 bar at idle but climbs properly to 110 bar under load so HPFP seems healthy. Coolant temp normal at 90°C. Codes are P2237 (persistent), P2240, P1127, P1129, P0133, P0153, P0136, P0156, P0068, P1158, plus P0491/P0492 that have always been there.

PCV was replaced at 180k km with a ÜRO (AC revision) so it has 52k on it. A week ago I made things worse by replacing 3 of 4 O2 sensors with cheap Amazon aftermarket because I assumed they were the problem. Now I’m stuck between theories: leaking injector on Bank 2 (fits the hot restart stall and bank asymmetry), exhaust leak from the shop weld affecting O2 readings, ÜRO PCV failing early, or some combination. The severity and timing point to the shop work triggering something, but I’m not sure if they directly damaged sensors or caused an exhaust leak.

Going to an Audi specialist this week for an injector leak-down test and physical inspection. Anyone seen this exact pattern on a B8 S4, or have experience with ÜRO PCVs failing early? Appreciate any insight before I walk in.

The other day i hooked up the scan tool to monotor the live data for misfires. As soon as i started driving cylinder 3 misfired one time drove to where i was going and when i got back as soon as i pulled in cylinder 4 misfired one time now 3 is on the passenger side and 4 is on driver side im going to swap coils and move them around and see if it follows and check plugs. If that doesnt work what should my next step be