If it fails to start and run right off the bat, you could have a fuel pump relay issue as mentioned above.

If it dies after driving 15-20 mi and won't start 'til it cools off, your elect. fuel pump(s) are shot. You either have 1 or 2 pumps - some 103 cars have 1; some have 2.

Another part to consider is the infamous OVP - overvoltage protection relay and finally, check all vacuum hoses - many opportunities here.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"