1991 Mercedes 300e hard starting

My 1991 300e, 170k, 6cyl, 4spd auto, will not start when cold. I have to use, gasp, starting fluid to get it going. When it warms up, it starts OK, it runs smoothly, no notable engine or belt noises, no overheating, shifts smoothly, accelerates a little slowly from standing start and at low rpm, but gets legs at about 3000 rpm. I am thinking fuel pump, but hate to start blindly replacing things. Any advice for trouble shooting and possible causes. Thanx