Thank you for the picture! Thanks everyone for quick responses, but since I don't know what most of the OTHER parts are that you mention, I really need the diagram.
You asked about symptoms. My car stalls a lot, especially at turns and stopping. After a turn or going uphill, I can press on the gas and nothing happens, then if I sort of pulse the gas pedal a little it will come back to life. If I haven't driven it for a day or so, it can be very hard to get it going in the morning--several starts, then restarting at each stop. There is a lot of spitting and inconsistent idling--if I stop for a while, it goes from normal to rough and then I stall. My mechanic adjusted the O2 sensor and it seemed better, then started acting up again. He replaced the air mass meter--same thing. He replaced the main fuel pump--same thing. Before returning, I'd like to have a clue so I don't end up replacing the entire car.