What causes Turbo Stall? Experienced it on the motorway in France when shifting down for a manouver. Is it a sign of problems or just the result of my poor driving ?

 

What's your definition of stall?! If you mean when you put your foot down after the gearchange you had to wait a second for boost to build then it's normal and you can learn how to avoid this. If it was longer and more pronounced then there's something amiss I'd say.

The turbo can stall if you suddenly shut the throttle with the turbo on boost, in severe cases it sends a shockwave back down the inlet tract which stalls the turbo (only momentarily if you then reapply the throttle quickly). I've found being more progressive with the throttle pedal movements helps, also you should be giving the throttle a blip on downchanges anyway!

 

Well, I shifted down to 4th to build up the revs prior to accelerating hard, when the traffic cleared I shifted to 3rd (blipping the throttle as usual) and planted my right foot for the usual launch. Instead of moving off the revs momentarily went to 5,500 rpm, then the turbo stopped spinning, revs dropped to 3,500 rpm and I had to wait for the usual lag (STI7 hence pick up around 4,000 rpm). First time I've had this in 4 years of Scooby ownership...