I believe that a characteristic of 16 valve 4-cylinder engines is that they seem to start out "slow" because the power band is in the upper rpm range.
As another thought, I've also noticed that Fords seem to be slow off the line initially & make up for it later....this is based on experience with 3 different Ford vehicles of different fuel injector/valves per cylinder/number of cylinders etc...just my 2 cents
