Engine cut-out on idle.

[Allan Wilson]

I have a BMW 5 Auto Tourer Estate 2011.  Tick-over very erratic - almost cutting out and sometimes does cut out whilst idling at traffic lights etc.  Also I can hear a slight and constant hiss (not a whistle like a turbo fault).  Any ideas what could be the problem.  Many thanks. 

[Greydog]

Hi Allan

Welcome to the Forum

The fact you can hear a hiss sounds like either an air leak (inlet manifold) or a vacuum leak 

Both will upset running a bit more information what engine diesel or petrol would help

Dave

[X5smw]

I agree with Greydog. 
have a look around the MAF sensor. A split between this and the engine block will give erratic air mixture. 
 

also, check the battery voltage … my x5 sometimes starts rough idling and revving when it’s a bit low and throws a throttle position sensor fault at me.