My C230 Kompressor has broken down twice in the.

My C230 Kompressor has broken down twice in the last 4 months - on both occasions it's felt like a fuel problem i.E. The car cuts out & grinds to a halt, but electrics are fine. The car turns over, but it won't fire & re-start - it's as if it has run out of petrol. On both occasions the car has restarted approx. 40 mins later and then run perfectly again. It almost feels like it needs to cool down even though there is no sign of overheating. I had it towed to a garage on the first breakdown and of course it started and they could find nothing wrong with it. It just happened again and I'm in the same situation. I feel it could be the fuel relay or pump - any ideas? Thanks!