'99 e320 sedan starting issue
 

My wife's car has an intermittant starting issue, after a short drive, and the car has been sitting for an hour or less, it will crank but not fire. It never does this first thing in the morning, for me, or after the car has sat for several hours.

Has 152000 miles, makes lots and lots of short trips, 2-3 miles.

Where would you start looking?

Thanks

Gary