Need Help Badly

[1.8turboIreland]

Hi All,
This is my first post here. I'm from Ireland and have a 1.8 Turbo Audi A4, 2000 reg.
We have a national car test here and my car failed, on it's C02 emissions and electronic throttle control, it wouldn't stay at 2500rpm.
I brought the car to a mechanic who had alook at it and replaced some parts in the turbo, the oxygen sensor, the waste gate regulator valve, top dump valve and bottom dump valve charged me 800euro and the car failed the test again. I'm major pi**ed off. Was I ripped off
I bought an engine error code reader and the following codes are showing up, 17536, Long term fuel trim bank 1 system too lean, 17956, Boost pressure control value open.
Can anyone help me diagnose the problem, please, as I won't be able to sell the car until this is fixed, and there is a 750euro fine for driving the car not having passed the National Car Test.

[A4TurboAvant]

i'm sure someone on here will be able to give you some advice, if you don't get any helpful replies try "audiforums.com".....