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I recently purchased a 2001 mk1 tt 225 Quattro and on our way home from picking it up it I noticed it was loosing boost on the highway. I first noticed it in 6th gear when I began to accelerate it would build maybe 5 psi and then you would start to hear pressure (for lack of better terms) pissing out from somewhere. It started loosing boost like that in 4th-6th gear at around 2.5k rpm. It would hold boost in 1st-3rd. At first, if you were accelerating hard and shifting up, it would hold boost in 4th. It sat for a couple weeks and when I went to drive it again, it started pissing boost 2nd and up when driving at lower rpms and would only hold boost if you accelerated hard from around 1k rpm. I am thinking that it could be the boost controller that is malfunctioning but I could be wrong as this is my first Audi and I am new to these. I hope I described the problem well enough to understand. If anyone has any ideas that could help me fix this problem it would be greatly appreciated. Thanks
Turns out, the previous owner had an N75j valve installed backwards on the car. I replaced it and it’s holding boost now but It threw a code(attached). Do I need to have it retuned because of the change in the boost controller or could it be a vacuum line or something of those sorts?
No it’s not a dangerous condition under normal driving. You need to check for boost leaks. The small hose from the end of the intake manifold to the fuel pressure regulator often leaks and will case this lean code.
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2001 TT 225 boost problem
