As above, sorry if a bit vague-that is because it is!

I have not seen the cutting out symptom but as one increases idle speed there is a distinct vibration at around 1500-2000 rpm but no smoking or any other obvious issues.

Apparently it restarts relatively easily after cutting out

Owner claims problems started after driving through water on the Motorway. I would be surprised if it had sucked water since the intake is well up in the engine bay (Sensible BMW!)

I am minded to check/change fuel filter for water and see how it goes.

Having said that the vibration bothers me!

Any other suggestions at this stage?