My 2007 Saab Convertible (20k miles) has twice been in the main dealers in the last month for a problem of the engine revs dropping below 500 r/p/m when reducing speed & dipping the clutch (also when steering at slow speed with the clutch depressed). This causes the engine to stop and is dangerous. They advise me that they have re-set the engine management system, but the problem re-occurs and require me to look at the rev counter each time the car is at low speed to ensure it is still running. Any thoughts as to cause? Thanks