1992 taurus wagon problems re-starting

my 1992 taurus wagon 3.6 liter recently had a tune up. and 3 months later has a problem starting after I make a short stop at the store. My first instinct was that it was flooded and would start after 5 min,but now it can take as long as 15-20 min before it starts. I found a broken vacum hose on the fuel injector header, and i replaced it but the problem still exists. Could it be my electronic fuel pump,sticky valve? i am lost with endless possibilities of causes. paul