I can't speak for the series 5 but i'm told the flooding problem was fixed by then. The rotary experts that fix my car and get all my hard ern't cash tell me the ECU is a piece of ****. Basically they drop a Wolf 3D in their and the problem vanishes, catch is their about $1500 AUD plus 10 hours of labour, vs a cheap assed toggle switch and a spare hour.

 

Yes, the stock computer is a piece of junk. You really notice the difference once an aftermarket computer is installed. Besides fixing the flooding problem, an aftermarket computer will give you much better throttle response and about 30hp more because you can chuck the stock airflow meter in the garbage. Also, it is really nice to be able to take full advantage of all your mods (exhaust, intake, etc.) instead of being stuck with the insufficient stock maps.