Idles OK when its cold but as soon as its slightly warm it cuts out.

Any ideas?

Thought it might be the MAF sensor??

Would seem a good place to start, can you get and diagnostic kit on it.

When I had issues with my S2 took it to local BMW place

Hi, diagnostics just read error codes and the RAC/AA can do that FOC, try Googling BMW 540i cuts out when hot and see what results you get. Having read some of the threads it would point towards the MAF.

if you unplug the MAF sensor, the ecu will revert to a default settling. Should the car perform normally with this disconnected, the MAF is at fault.

Or it may just be poor connections to the MAF itself...

Cheers,

Had that on my S1 - Air Mass sensor fault
Keith @ BHM diagnosed it over the phone!

Had a similar fault on another car. Replaced the MAF to no avail, and tried a few other things too. Problem persisted... until we looked at the catalyst! The matrix had broken apart and a large 'lump' was loose in the housing. After a short period of running the lump had been pushed by exhaust gas into the exiting pipe, blocking it - result, engine died. It wasn't until after some cooling that the lump fell back to re-open the pipe.
Almost certainly not your problem but an interesting variation all the same - that took some finding.
Terry (+8)

Hello Viper

Did you get to the bottom of your problem?

I replaced the MAF on my S1 three years ago, though the symptoms were very different; I had one cylinder bank running rich, which, I don't understand since there is only one MAF that feeds info to ECU.

For info, though car couldn't be more different, Just replaced the crank position sensor on another car (Smart City Coupe) after similar symptoms to yours, e.g. engine cutting out when warm. Problem solved.

Cheers

Philip

Just replaced the Crank Sensor on the Smart for same reason. sorted

Calling Viper. The suspense is killing me, what was the problem?

Cheers