I've been reading and reading and reading the previous posts here and other locations, but I'm still at a loss on what cause this fault and wonder if anyone can help.
I know it's a lot of text but I wanted to be clear on what I've done already so nothing was suggested that i have already done.
A little history:
Car has been going into limp mode for months and with what i can only describe as a steam train puffing noise, the car would judder under pressure when cold. This went on for weeks and recently it has stopped but started to over boost after i fitted a new MAF through Audi's recommendation. The juddering continued and finally fizzed out after i put in a new MAF. At the time, I didn't know it was over boosting and assumed that the car was working as it should. Audi had the car for 4 hours testing it and came up with multiple faults including, turbo, MAF, and N75 valve.
After replacing the N75 valve the car continued to over boost. So far all the vac pipes have been replaced, the waste gate has been checked which was fine including the pipe to it, fuel and air filters replaced along with the solenoid valve. All parts have come from Audi directly. The EGR has been taken apart twice and cleaned with carburetor cleaner and I've watched it work with the inter cooler pipe off and although seems a little sluggish (difficult to find videos on how it should look when working) I've continued to use it rather than replace it at this stage since i think its ok.
The engine codes have come back with solenoid value going to ground and that's it. I've replaced this-no effect.
I took the car out for a test run Wednesday and the turbo blew, white smoke and oil coming out of the exhaust. The inter cooler has been checked tonight and oil has been found in it. I've cleaned this out with turps and made sure the pipes are clear; so first question; is this acceptable?
I'm still trying to find a turbo without much success atm. Secondly, I'm at a complete loss why the turbo blew in the first place. I did check it not 2 weeks ago and the fan moved slightly but i was told by a family mechanic of 30 years experience, that this was OK as its due to wear n tear so that is acceptable(?). I've looked everywhere for an answer and from what i can tell I've replaced everything that would cause this apart from the EGR value.
To be honest I'm totally fed up with the car despite it being in fantastic condition for its age and I will be selling it as soon as I fix it. I'd just like to know what could have caused it so that i can fix it for the new owner so the turbo doesn't blow again and for my own peace of mind/sanity.
Many thanks and sorry for the amount of text.