99 mercury cougar wont start?

Replaced, camshaft positioning
sensor, spark plugs and wires, coil
pack, starter, alternator, fuel pump,
fuel filter, and the pressure regulator.         
After sitting for a while it will crank,
but just wont start. But sometimes if I
hold the gas all the way, it will start,
and idle funny and have a huge cloud
of dense white smoke. Smoking goes
away, idle returns to normal, and it
runs fine.........      still the car sits for a
while.