M104 1992 stalling out - fuel or ignition?

[nevremj]

1992 300ce with 104 engine. While driving at operating temp, car will start running rough and it feels weak. after about 2 minutes or so it stalls out and won't restart. tow to mechanic he inspects ignition system(plugs look new). Installs new coil. Car runs great. Weeks later same stall out. And yet a third time several weeks later. Mechanic checks it out - can't find anything. I pick up the car - starts ok and runs for about 10 minutes then same thing. About two hours later it starts ok and I drive it for a few minutes around the neighbor hood OK.
The issue is that stall outs can't be predicted, but after car sits following a stall out it starts ok.
I feel like its fuel - filter, pump, whatever.
Any hints on how to diagnose the problem -
Any help greatly appreciated - help keep car from the crusher