Cutting-out when hot - Can anyone help?
 

My 1995 E280 (W124 24 valve) has started cutting out when warm. It's usually when travelling at 50 mph or so. The car loses all power and starts to slow - but whilst slowing, the tachometer starts "jumping about" between 2000 and 5000 rpm but the engine isn't revving up at all.

If I try to start the engine straight away, it won't start but the tachometer "jumps about" as before.

If I leave it for maybe ten minutes, it starts immediately and runs fine. No other symptoms - it runs really well all the rest of the time.

Tonight, it decided to stop on the M25, so it needs sorting out sharpish!

I'm assuming it's as electrical fault......can anyone tell me what mysterious "black box" may be at fault!

Thanks, Doug