Recently replaced gearbox in this mini cooper s cabriolet. Put everything together, engine starts first time, idles beautifully whilst in 'park' or 'neutral' but as soon as you engage the automatic gearbox in 'reverse' or 'drive' the engine starts spluttering and stalls - has anybody got any ideas???? Thanks Jo

 

I would suspect a serious vacuum leak. Not familiar with the trannies on the Mini so I couldn't point you to a specific location, but check in that direction. Otherwise I have to ask about the transmission itself. Does the car attempt to move while it's sputtering?