Random boost problems
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Joined: Jul 2022
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Random boost problems
Hi everyone. Sorry ahead of time for the kinda long post. I‘m lost at this point.
Quick background; I work on cars for a living, both mechanical and autobody, for over 25 years and I do work on Audis and other European cars all the time. That being said, I have a stock 2004 A4 1.8t Awd 6 speed. My boost comes and goes when it pleases. And it’s driving me crazy. I have a boost gauge in my car. When it’s working fine I get about 9-10psi. When it’s not I only get 4psi. It happens randomly. When it’s working fine it will be good all day if I don’t turn the car off. As soon as I turn the car off then I only get 4psi. But some days it will work all day no matter what. Some days it won’t work at all. Some days it won’t work then work a few minutes later. I’ve changed the Map sensor and diverter valve. No change. I’ve ran vacuum and boost tests and everything was good. I scanned the whole system with my snapon scanner and everything checks out ok. The only other problem I have is my idle sometimes is high, like 1100-1200. I cleaned the throttle body and relearned it to the car and no changes. At this point I’m hoping someone had a similar problem and can point me in the right direction. Please help!
Quick background; I work on cars for a living, both mechanical and autobody, for over 25 years and I do work on Audis and other European cars all the time. That being said, I have a stock 2004 A4 1.8t Awd 6 speed. My boost comes and goes when it pleases. And it’s driving me crazy. I have a boost gauge in my car. When it’s working fine I get about 9-10psi. When it’s not I only get 4psi. It happens randomly. When it’s working fine it will be good all day if I don’t turn the car off. As soon as I turn the car off then I only get 4psi. But some days it will work all day no matter what. Some days it won’t work at all. Some days it won’t work then work a few minutes later. I’ve changed the Map sensor and diverter valve. No change. I’ve ran vacuum and boost tests and everything was good. I scanned the whole system with my snapon scanner and everything checks out ok. The only other problem I have is my idle sometimes is high, like 1100-1200. I cleaned the throttle body and relearned it to the car and no changes. At this point I’m hoping someone had a similar problem and can point me in the right direction. Please help!
Thread Starter
AudiWorld Newcomer
Joined: Jul 2022
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yes, I did the thing where you clamp off the line for the n75 valve and it will overboost so the wastegate works fine. That’s what is random about it and that’s why I’m stumped. I’ve done all the reasonable tests I could think of and read about and no obvious problem has shown itself. Some days the turbo works perfectly fine so it’s almost like it’s an electrical issue where the wastegate is being told to open at 4-5psi instead of 9+psi.
AudiWorld Member
Joined: Dec 2021
Posts: 95
Likes: 12
From: UK
If you have VCDS you can log the boost and Items that relate to boost control pressure to narrow down what is causing this to happen. Have you checked for intermitant DTC's? I would also check the wiring to the N75 valve.. 18 year old wiring! My 02 A4 1.8T isshowing wiring gremlans now.
Last edited by Larhal; Jul 10, 2022 at 08:43 PM. Reason: Additional info
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