My BMW 116i has a temporary loss of power when accelerating in first and second gear (between around 1500rpm and 2000rpm). It feels as though the turbo is not working (it normally has very linear acceleration). This only happens when the engine is first started from cold and the problem is gone within 1 minute of driving. When the power does come back, the turbo kicks in quite violently making for very uneven acceleration. Any thoughts what might be the issue? I always run the car on Shell V Power Nitro+ and have covered 32000 miles.