While driving my 1988 Mercedes 2.3 190 E on the interstate highway at 60 mph for about 15 minutes or so the car stalls...... ?? I pull over onto the emergency lane put my flashers on turn the key off and wait about 2 minutes and the car starts OK and runs OK. I drive it for a day or longer and nothing happens. Then all of a sudden again it stalls out on me while driving..... When it stalls it is at different speeds,,,,, My trouble-shooting has lead me to replacing the crankshift sensor, front TDC sensor, fuel filter, and ignition coil and still stalls out on me. I orderd a new fuel pump and will install it. Please advise me of the next steps to take in trouble-shooting my car problem....... Thanks!