I've been facing this intermittent sudden power loss for quite sometime. I have a 54 reg Audi A3 140 BHP that has done 110 K. I can drive my car at around 80 MPH(mostly in cruise control) for an hour without any issues. Then the car suddenly looses power. If I restart all is fine. However, I could see the Engine management light turning ON at times. This is occurring more frequently after the Authorized Audi dealer replaced my intercooler citing turbo leak when I complained of slight sluggishness. Recently the Audi dealer replaced the N75 valve too. Even after spending more than 1000 bucks the problem persists. Now the so called authorized dealer feels there is a turbo overboost and the complete unit has to be replaced(another 1200 in drain).
I've lost confidence in these guys and am really not sure if a turbo failure is the cause for this intermittent failure and replacing this would resolve the problem. Kindly share your thoughts if something as trivial as MAF would do the trick or the symptoms indeed point to a turbo replacement. Appreciate if somebody can suggest a garage(specialist) in West London who've fixed similar complaints.